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Browning Machine Gun .50 Caliber M2 History
Browning .50 Cal M2 HB Quad Mount

Browning .50 Cal M2 Water Cooled
Browning .50 Cal M2 Water Cooled

Browning .50 Cal M2 Heavy Barrel on quad mount with tombstone ammo drums
Browning .50 Cal M2 HB

Early Browning .50 Cal M2 HB
Early Browning .50 Cal M2 HB

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Update 3rd August 2009, "The Machine Gun" by George Chinn, Lieutenant Colonel, USMC is available online here: http://www.ibiblio.org/hyperwar/USN/ref/MG/index.html

The following excerpts were gathered from military publications used in my research and are non-PT boat specific. I've included them on this site for historians, restorers of WW II guns (early part numbers), and to help you ace games of BMG trivia.

About the difference between the words "materiel" and "material" as found in military documents, the definition from Wikipedia:
Not to be confused with Material.
Materiel (from the French "matériel" for equipment or hardware, related to the word material) is a term used in English to refer to the equipment and supplies in military and commercial supply chain management.
In a military context, materiel relates to the specific needs of a force to complete a specific mission. The term is also often used in a general sense ("men and materiel") to describe the needs of a functioning army.
Materiel in the commercial distribution context comprises the items being moved by the services of or as the products of the business, as distinct from those involved in operating the business itself.

Book Excerpts

From the 1951 naval publication "The Machine Gun":

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The Machine Gun
History, Evolution, and Development of Manual, Automatic, and Airborne Repeating Weapons
by George Chinn, Lieutenant Colonel, USMC
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TMG Chinn Automatic Aircraft Gun T Number Assignments

Comparative Data: Browning Caliber .50 M2 Gun
CharacteristicBasicHeavy barrelWater cooled
Gun length (inches)56.125.65.125.65.93.
Gun weight (pounds)61.81.121.5 (with water).
100.5 (without water).
Rate of fire (rounds/minute)750-850.400-500.600-750.
Muzzle velocity:
   feet/second
   miles/hour
 
2,845.
1,940.
 
2,935.
2,000.
 
2,935.
2,000.
System of operationShort recoil.Short recoil.Short recoil.
System of lockingRising block.Rising block.Rising block.
System of feedingBolt actuated.Bolt actuated.Bolt actuated.
Method of headspaceRotation of band.Rotation of band.Rotation of band.
Location of feed openingRight and left side (top).Right and left side (top).Right and left side (top).
Location of ejection openingBottom of receiver.Bottom of receiver.Bottom of receiver.
Method of chargingManual, hydraulic, or air.Manual, hydraulic, or air.Manual, hydraulic, or air.
Method of cooling.Air.Air.Air.
Barrel length (inches).36.45.45.
Barrel weight (pounds)10.27.4.16.
Rate controlMuzzle booster can be installed.Drain oil buffer.Drain oil buffer.
Barrel removal.Quick disconnect.Quick disconnect.Quick disconnect.
Bore:
   Number of grooves
   Groove depth
   Groove width
   Pitch
   Direction of twist
   Form of twist
   Number of lands
 
8.
0.015.
0.110.
1 turn in 15 inches.
Right hand.
Constant.
8.
 
8.
0.015.
0.110.
1 turn in 15 inches.
Right hand.
Constant.
8.
 
8.
0.015.
0.110.
1 turn in 15 inches.
Right hand.
Constant.
8.
Weight of bullet:
   Grains
   Ounces
 
712.
1.62.
 
712.
1.62.
 
712.
1.62.
Weight of powder charge:
   Grains
   Ounces
 
250.
0.57.
 
250.
0.57.
 
250.
0.57.
Weight of cartridge (ounces)4.20.4.20.4.20.
Weight of 100 cartridges in
metallic links (pounds)
30.25.30.25.30.25.
Maximum range:
   Yards
   Miles
 
7,200.
4.1.
 
7,600.
4.3.
 
7,600.
4.3.
Source: The Machine Gun by George Chinn, Lieutenant Colonel, USMC
The following tabulation lists the various models and bores of Browning recoil-operated machine guns that have been produced for use by the nations of the world:
Models of Browning Recoil-Operated Machine Guns
NameCountryDesignationBore
Browning groundU. S. A.Model 191730/06
Browning groundU. S. A.Model 1917A130/06
Browning trainingU. S. A.M1.22
Browning tankU. S. A.M2.30/06
Browning trainingU. S. A.M3.22
Browning trainingU. S. A.M4.22
Browning tankU. S. A.M1919.30/06
Browning tankU. S. A.M1919A1.30/06
Browning cavalryU. S. A.M1919A2.30/06
Browning gen. purp.U. S. A.M1919A3.30/06
Browning gen. purp.U. S. A.M1919A4 early.30/06
Browning gen. purp.U. S. A.M1919A4 later.30/06
Browning tankU. S. A.M1919A5.30/06
Browning groundU. S. A.M1919A6.30/06
Springfield groundU. S. A.Experimental.30/06
Rock Island groundU. S. A.T13.30/06
Colt groundU. S. A.Experimental.30/06
Browning groundU. S. A.M1919 w/c.30/06
Browning aircraftU. S. A.M1918.30/06
Browning aircraftU. S. A.M191811mm
Browning aircraftU. S. A.M1918M1.30/06
Browning aircraftU. S. A.M1919.30/06
Browning aircraftU. S. A.M1921.30/06
Browning aircraftU. S. A.M1922.30/06
Browning aircraftU. S. A.M2.30/06
Browning infantryMexicoM19197 mm
Browning infantryArgentinaM19287.9 mm
Browning infantryPolandM19307.9 mm
BrowningBoliviaCommercial type7.65 mm
Browning infantryChinaCommercial type7.9 mm
Browning groundNorwayM19297.9 mm
Browning groundNorwayM1929T7.9 mm special
Browning groundSwedenM19366.5 mm
Browning groundSwedenM19367.9 mm
Browning groundGuatemalaM19247 mm
Browning groundGuatemalaM1942.30/06
Browning tankJapanType 47.7 mm
Browning tankJapanType 977.7 mm
Browning aircraftNorwayM19297.9 mm
Browning aircraftGreeceM19377.9 mm
Browning aircraftFranceCommercial type7.5 mm
Browning aircraftEnglandMark II7.7 mm
Browning aircraftEnglandMark II*7.7 mm
Colt groundCommercialMG 38Various
Colt groundCommercialMG 38BVarious
Colt aircraftCommercialMG 40Various
Colt groundCommercialMG 52.50
Colt groundCommercialMG 52A.50
Colt groundCommercialMG 52-2.50
Colt aircraftCommercialMG 53.50
Colt aircraftCommercialMG 53A.50
Colt aircraftCommercialMG 53-2.50
BrowningCommercialFN.50
BrowningCommercialFN13.2 mm
Browning AAU. S. A.M1921.50
Browning AAU. S. A.M1921A1.50
Browning AAU. S. A.M2.50
Browning AAU. S. A.M2 Navy special.50
Browning aircraftU. S. A.M1921.50
Browning aircraftU. S. A.M2.50
Browning aircraftU. S. A.M2 Navy special.50
Browning groundU. S. A.M2 HB.50
BrowningU. S. A.M2 HB Navy special.50
Browning aircraftU. S. A.M2 TT.50
Browning aircraftU. S. A.M3.50
Browning groundGuatemalaM1924.50
Browning groundGuatemalaM1942.50
Browning aircraftJapanModel 1.50
Source: The Machine Gun by George Chinn, Lieutenant Colonel, USMC
Section 2. Characteristics of United States Large-Caliber Automatic Guns / Caliber .50 Machine Guns

TMG Chinn .50 cal T Model Number Images

Gun, Machine, Caliber, .50, Model 1918.
In April 1918 the AEF, in a cable to the War Department, expressed an urgent requirement for a high-powered, large-caliber machine gun and ammunition primarily for aircraft, with second priority for ground use. Available knowledge on the performance of a German 13.2-mm rimmed antitank cartridge, as well as information on the British development of a caliber .50 cartridge, led to a decision to develop a caliber .50 machine gun and ammunition. Guns were designed under the supervision of John Browning at the Colt's Patent Fire Arms Manufacturing Co. (ground type) and at the Winchester Repeating Arms Co. (aircraft type). (See The Machine Gun, vol. 1, p. 335.)
Gun, Machine, Caliber, .50, Model 1921.
This series of Browning guns were the first standard machine guns of caliber .50 to be adopted by the United States Government. There were variations for ground, air, and naval use. All this material is now obsolete.
Gun, Machine, Caliber .50 T1.
An early design in the program to modify the Browning caliber .50 gun to permit right and left-hand feed. Both air-and water-cooled guns were made.
Gun, Machine, Caliber .50 T2.
An intermediate stage in the development of the caliber .50 M2 series.
Gun, Machine, Caliber .50 T21.
The Browning T21 was a collaborative effort by Colt and Springfield. This weapon underwent tests at Aberdeen Proving Ground from 1940 to 1942 with unfavorable results. The importance of that project was the establishment of a standard of performance for an acceptable high-speed gun. One breakage and five malfunctions were to be permitted in 5,000 rounds of firing at 1,200 rounds per minute.
Gun, Machine, Caliber .50 T22.
Early in 1942 the High Standard Manufacturing Co. designed a high cyclic rate caliber .50 Browning machine gun and made two models. These guns, designated T22, were submitted to the Aberdeen Proving Ground for test 10 August 1942. One gun was fired on that date, 554 rounds at a cyclic rate of 1,066 rounds per minute, during which five stubbed rounds and two failures to feed occurred. Both guns were returned to High Standard for modification. A total of 10 guns were made.
Gun, Machine, Caliber .50 T22E1.
This was a version of the T22 tested February 1943 which failed after firing 111 rounds. Failure was due to a broken sear.
Gun, Machine, Caliber .50 T22E2.
Tested in March 1943 this gun fired 3,700 rounds at cyclic rate of 1,219 rounds per minute. There were 43 malfunctions and 7 breakages.
Gun, Machine, Caliber .50 T22E3.
The records do not indicate the history of the T22E3.
Gun, Machine, Caliber .50 T22E4.
Tested in August 1943 this gun fired 5,000 rounds at a cyclic rate of 1,108 rounds. There were 36 malfunctions and 2 breakages.
Gun, Machine, Caliber .50 T22E5.
Modification of T22E4. Two guns were produced but when fired at Aberdeen their rate of fire was less than 1,000 rounds per minute.
Gun, Machine, Caliber .50 T22E6.
Tested late in 1943 the T22E6 first gave poor results. Inthe development of this gun an effort was made to hold to a minimum the changes from thestandard Browning M2 gun. Because of defects inherent in the mechanism it was decided that further development could not be expected to produce a completely acceptable weapon. Accordingly, further development of the T22E6 gun, as such, was not undertaken by the Ordnance Department although certain features of the weapon were incorporated in the T36 (M2A1) and T25E3 (M3) guns.
Gun, Machine, Caliber .50 T25.
In the development of the T25 by Frigidaire no restriction was placed on the number of changes, from the M2 gun, and the contractor was permitted to proceed by making all changes necessary to provide reliable functioning at a rate of fire of 1,200 rounds per minute. For example, the backplate buffer, barrel buffer, and receiver were redesigned. It was not until 10 March 1944 that the first T25 gun was submitted to Aberdeen Proving Ground for test. The gun gave a fair performance for 2,000 rounds, but from that point on excessive breakages and malfunctions occurred, and at 3,100 rounds the test was discontinued because of the breakage of the backplate buffer.
Gun, Machine, Caliber .50 T25E1.
Work was immediately started on a second gun, the T25E1, which was tested at Aberdeen 10 May 1944. This gun was completely unsatisfactory. Nine breakages and three malfunctions occurred in 770 rounds and the test was stopped. Satisfactory functioning had not been obtained with the T25 series guns but certain features of those guns were considered very desirable.
Gun, Machine, Caliber .50 T25E2.
To permit further study of the causes of this unsatisfactory functioning, the T25E2 gun was made up by substituting the bolt, top cover and recoil booster of the T22E6 gun for corresponding components of the T25E1 gun. This gun was fired at Aberdeen Proving Ground in June 1944. Functioning continued unsatisfactorily, and the test was stopped at 1,800 rounds. A careful examination indicated that the nested helical springs in the backplate buffer were breaking and causing extreme impact forces on the gun component.
Gun, Machine, Caliber .50 T25E3.
The first T25E3 gun was tested at Aberdeen 19 July 1944. The functioning of this gun was greatly improved over that of the T25E1, and the cyclic rate averaged 1,250 rounds per minute. Eight malfunctions occurred, hut for the first time in the development, it was possible to determine the specific cause of each malfunction. A projecting corner on the bolt was responsible for "shorting" rounds in the feedway and causing failures to feed; the remainder of the malfunctions were caused by fatigue of the sear spring. After the satisfactory test's of the T25E3 guns, and to expedite procurement of this weapon, the Army Air Forces requested its standardization in April 1945. Ordnance Committee action was immediately taken to standardize the T25E3 gun as Gun, Machine, Caliber .50 M3, Aircraft, Basic.
Gun, Machine, Caliber 50 T26.
Modification of the Browning M2 gun produced and tested at Aberdeen. Included a short-round device submitted by the Army Air Force and the cover assembly of the T22E5. The extractor assembly was also taken from the T22 series as was the backplate assembly. A muzzle booster with a 0.65-inch hole was used and a pneumatic buffer and a modified sideplate switch.
Gun, Machine, Caliber .50 T27.
This was a Browning developed by High Standard to provide a kit of parts which could be used to convert the standard M2 gun to a high-speed weapon. The test was stopped before completion in January 1944.
Gun, Machine, Caliber .50 T27E1.
Unsatisfactory performance, since one of the two guns made blew up. Test discontinued about February 1945.
Gun, Machine, Caliber .50 T27E2.
The records do not indicate that the history of the T27E2 extends beyond the blueprint Stage.
Gun, Machine, Caliber .50 T27E3.
Tested in March 1944; numerous malfunctions.
Gun, Machine, Caliber .50 T27E4.
Fired at a rate of 1,330 rounds per minute when tested in April 1944 but suffered numerous breakages and malfunctions.
Gun, Machine, Caliber .50 T27E5.
Tested in June 1944; excessive malfunctions terminated the test after the one gun blew up.
Gun, Machine, Caliber .50 T27E6.
Tested early in 1945, it successfully fired 5,000 rounds at a rate of over 1,000 rounds per minute with only one breakage of major parts but 1 of the 4 guns tested had 11 malfunctions.
Gun, Machine, Caliber .50 T27E7.
In March 1945 the last version was tested and successfully completed the 5,000 round test without going beyond the numbers of acceptable malfunctions but suffered excessive breakage of minor parts. In the overdevelopment of the T27 series, unsatisfactory performance and danger to personnel and equipment caused by the unusual number of breakages and explosions were responsible for the decision in March 1945 that no further consideration would be given this weapon.
Gun, Machine, Caliber .50 T28.
Developed by Springfield Armory to produce a high cyclic rate gun. Specifications called for 1,200 rounds per minute without breakages.
Gun, Machine, Caliber .50 T34.
Air Force requirement for the fabrication of a gun which would have a cyclic rate of 1,500 rounds per minute. Project assigned to Springfield. This was to be an entirely new mechanism, operating on a principle suitable for very high-speed operation. Preliminary drawings of this gun were received in August 1945, and after careful study, the Springfield Armory was requested to supply additional drawings.
Gun, Machine, Caliber .50 T35.
To fulfill the Air Force requirement for a gun with a cyclic rate of 1,500 rounds per minute, a project was set up to modify the M2 Browning.
Gun, Machine, Caliber .50 T36.
During the development of a high speed caliber .50 machine gun, certain very valuable improvements were made which were applicable to the standard M2 caliber .50 aircraft gun. In September 1944, it was decided to incorporate immediately into the M2 gun these features which had been proven in tests of various experimental high speed guns. This improved gun, designated T36, was designed to accomplish limited objectives, compared to the M2 gun, namely: (1) reduction in recurrent malfunctions; (2) increase in cyclic rate of approximately 100 rounds per minute; and (3) increase in belt lift capacity to 30 pounds minimum consistent with the accomplishment of these objectives.
Gun, Machine, Caliber .50 T38.
A further development of the M3 by Frigidaire in 1945. This design was also in response to the Air Force requirement for a 1,500 round per minute gun. Limited firing was conducted at rates up to 1,450 rounds per minute by Frigidaire.
Gun, Machine, Caliber .50 T42.
Intended for use as an antiaircraft weapon with a rate of fire of 700 rounds per minute. Similar to the Browning M3 but uses heavy barrel and short barrel support.
Gun, Machine, Caliber .50 T60.
This was a project set up in 1948 to develop an aircraft gun with a rate of fire 2,000 rounds per minute.
Gun, Machine, Caliber .50 T164.
The armored force established a requirement for a caliber .50 machine gun for use on tank turrets with the provision that it must incorporate a short receiver. Springfield Armory built a revolver type based on the 20-mm T74 and this is designated the caliber .50 T164.
Gun, Machine, Caliber .50 T175.
Similar to the T176, except barrel energy is transmitted by hydraulic means. Also intended for tanks.
Gun, Machine, Caliber .50 T176.
The T176 was designed in response to the requirement for a short receiver tank gun. It is a nonconventional type in which the barrel energy is used to operate the mechanism indirectly through Belleville springs. It was designed for alternate use at a high and low rate of fire.
Gun, Machine, Caliber .50 M1.
The experimental Browning T2 caliber .50 machine gun was standardized for cavalry and infantry without modification as the M1. This model never went into production.
Gun, Machine, Caliber .50 M2.
Further development of the Browning system produced the M2 series which was standardized in 1933. The three principal versions were water-cooled, aircraft, and heavy barrel. The three guns utilized the same basic receivers. The water-cooled gun was for antiaircraft use; the heavy-barrel gun was intended for use by and against armored vehicles, and the aircraft gun with its 36-inch air-cooled barrel was for use in aircraft. Later, several other varieties were standardized, all of which used the same basic receiver. An important characteristic of the M2 series is the ability to convert from one type to another.
Gun, Machine, Caliber .50 M2A1.
In 1944, the limited procurement of 31,336 of the T36 guns was authorized. This procurement was discontinued after approximately 8,000 guns had been produced because of the unexpected progress made in the development of the T25E3 high-speed gun, which led to its standardization as the M3 earlier than had been thought possible. Following the standardization of the M3 gun, the T36 gun was reclassified as limited standard, and redesignated Gun, Machine, Browning, Caliber .50, M2A1, Aircraft, Basic.
Gun, Machine, Caliber .50 M2E1.
The records do not indicate the history of the M2E1.
Gun, Machine, Caliber .50 M3.
In 1945 the caliber .50 Browning T25E3 was standardized as the M3. There are slight variations in guns of early and later manufacture. The M3 gun is based upon the caliber .50 aircraft machine gun M2 and has essentially the same exterior dimensions, except for the increased diameter of the backplate buffer, and the length added by the recoil booster. It fires at a cyclic rate of approximately 1,200 rounds per minute with standard ammunition and links. Nearly all parts of the M3 gun differ in detail from those of the M2, having been improved in design and metallurgy.

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From the military book series "The United States Army In World War II" aka "United States Army Green Books".

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The United States Army In World War II: Procurement And Supply
by Harry C. Thomson and Lida Mayo
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Chapter VIII, Small Arms / Machine Guns

With about 140,000 machine guns left over from World War I, the Army felt no urgent need for new production during the 1920's and early 1930's. As time went on, the various wartime types - Lewis, Vickers, Marlin, and others - were one by one declared obsolete, though prudently kept in storage for an emergency, until only the Browning models remained as standard. At Springfield and Rock Island the M1917 Brownings were modified and given new designations, M1917A1 (watercooled) and M1919A4 (air-cooled). The one outstanding machine gun development of these years was the redesign of the .50-caliber Browning machine gun so that it could be quickly converted to serve as tank, aircraft, or antiaircraft weapon. The heavy barrel of the tank gun, the waterjacket barrel of the AA gun, or the lighter parts of the aircraft gun could be attached in a matter of minutes without modification of the basic receiver. This simplified design, adopted in 1933, eased manufacture, maintenance, and troop training throughout the war.

Of the commercial gunmaking firms in the United States, only Colt retained active interest in machine guns during the interwar years. Under contract with Ordnance, it made production studies on Browning guns, both .30-caliber and .50- caliber, and contributed to the preparation of descriptions of manufacture. In 1939 Rock Island installed a production line capable of turning out .30-caliber machine guns at the rate of twenty five per day, and Ordnance placed production orders with the Savage Arms Company of Utica, N.Y., and with four divisions of General Motors - Saginaw Steering, Frigidaire, AC Spark Plug, and Brown-Lipe-Chapin. The British placed contracts with Colt and three other firms to make machine guns for planes and tanks being built in the United States for the British Army, and to all these firms Ordnance released its latest designs. Thus, total machine gun production capacity created during the defense period for the U.S. Army and its allies was considerable. By Pearl Harbor, Ordnance had contracted for annual production of some 430,000 .30-caliber and 300,000 .50-caliber guns, and ten plants, including Rock Island, were in production. supported by scores of subcontractors.

When President Roosevelt announced his "must" program in January 1942, he called for the production of 500,000 machine guns each year for the next two years. The War Munitions Program of February 1942 put total requirements at 1,302,000 for 1942-43 and the first half of 1944. To meet the demand for aircraft guns Ordnance found itself well prepared; it was able to report in February 1942 that output of caliber .50's was running well ahead of plane production, so far ahead, in fact, that caliber .50's were being mounted on 37-mm. AA carriages as additional weapons. General Wesson had told his staff earlier: "Forget everything else, but be sure you have a gun on every plane that comes out of this country; I don't care where it goes, I want a gun for it." For ground machine guns, capacity was below requirements early in 1942 but tank objectives dropped during the year, bringing a corresponding drop in ground machine gun requirements. By the end of the year production of all types, both air and ground, totaled 662,331, just enough to meet requirements. The most sharply defined trend was the shift from the small .30-caliber to the powerful .50- caliber aircraft machine gun with armorpiercing, incendiary ammunition. (Table 16) Hidden within these over-all figures were many stops and starts as requirements were cut and factories shut down at one point only to be followed by an emergency demand for new production a few months later.

The .50-caliber aircraft gun program reached its peak during early 1944 when production capacity rose to 45,000 per month, just enough to meet the Army Supply Program requirement of 540,000 for the year. With 1945 requirements set at 747,000 guns, Ordnance planned to build two additional plants, but dropped the matter during the second half of the year when requirements were cut and surplus machine guns piled up in Field Service warehouses. The contract with the Buffalo Arms Corporation, a high-cost producer in a tight labor area, was terminated early in 1945, and Kelsey-Hayes was put in a standby status.

Machine Gun Production, from July 1st 1940 to Aug 31st 1945
Caliber 1940 1941 1942 1943 1944 1945 Total
.50 (all types) 5,155 49,479 347,492 641,638 677,011 239,821 1,960,596
.30 (all types) 3,633 27,672 314,839 188,331 121,771 62,977 719,223
Source, yearly totals: Whiting, Statistics, Table PR-8

Production engineers worked miracles in simplifying processes, saving material, and speeding production of machine guns. Rifling broaches more than cut in half the time required for rifling barrels. Pearlitic malleable iron castings, known as Arma steel, not only saved scarce steel alloys but proved superior to the steel or bronze originally used for certain machine gun parts. Substitution of castings, stampings, or a combination of stamped and riveted parts for completely machined parts saved countless man-hours and machine-toolhours, and resulted in lower costs. There were problems, too, that had to be ironed out through the Machine Gun Industry Integration Committee. Some problems stemmed from the fact that commercial machine gun production had been on a small scale during the preceding two decades, and had been limited to one manufacturer. Colt's small peacetime orders had not warranted extensive application of mass-production techniques. Tolerances, specifications, and inspection rules had not been worked out in sufficient detail to guide numerous producers unfamiliar with gunmaking, nor were the rules always applied in the same way. The General Motors plants, for example, complained that inspectors were rejecting parts for exceeding tolerances on the drawings although the parts were identical with those taken from sample guns made by Colt. Tripods were the chief bottleneck in 1941 and could be turned out in adequate quantities only by adopting less complicated designs. An Army inspecting officer reported in April 1943 that, although production to date had been "extremely satisfactory," some of the older plants clung to outmoded methods, resisted change, and were generally less efficient than the newcomers. But, all things considered, machine gun production was one of the most successful features of the whole Ordnance program.

Chapter IX - Small Arms Ammunition
Small Arms Ammunition Production, 1940-1945
Size Quantity (in rounds)
Caliber .60 6,100,000
Caliber .50 10,042,259,000
Caliber .45 4,072,000,000
Caliber .38 187,000,000
Caliber 9-mm 548,600,000
Caliber 7.92-mm 798,800,000
Caliber .303 1,068,000,000
Caliber .30 25,065,834,000
Total 41,788,593,000
Source: Whiting, Statistics, p. 51.
Ammunition Belts

To manufacturers, metallic belt links were deceptively simple in appearance. Each steel link consisted of three small loops, two on one side and one on the other. A belt of ammunition was formed by placing the single loops of one link between the two loops of the other and inserting the cartridge through the three loops in much the same manner as one slides a bolt through the hinge of a screen door. Any number of links could be assembled in this manner to make a long belt of cartridges that had great flexibility and could be rolled and twisted to fit confined spaces in airplanes.

In addition, the belt links automatically fell apart as the cartridges that held them together were fired and ejected from the gun. Thus the origin of the term "disintegrating metallic belt links." Though simple in design these metallic links demanded exceptional accuracy in piercing, cutting, forming, and heat-treating to guarantee faultless performance when used in aerial combat. If links were too hard they were likely to break under pressure, and if too soft they might stretch and cause stoppage of the weapon. If either too loose or too tight they would not function properly. As rust or corrosion on links would render them unfit for use, they had to be given a carefully controlled rustproofing treatment before being sent to the field. Rigid inspection was essential to guard against acceptance of a single link that might cause trouble, for it was literally true that an ammunition belt was only as strong as its weakest link. During the years of peace Rock Island Arsenal was the sole producer of links in the United States. As there was but a trickle of new ammunition produced each year the need for links was correspondingly small, but during 1940 Rock Island turned out about 50,000,000 .30-caliber links and about 15,000,000 .50-caliber. With requirements for aircraft ammunition on the rise, and with a shift toward the larger caliber taking place, Rock Island placed contracts with industry for .50-caliber links, beginning in June 1940 with the Fort Pitt Bedding Co. and three other concerns in 1941. Approximately 150,000,000 were produced in 1941, three times the 1940 output. In the summer of 1941 production of .30-caliber links began at Jackes Evans Manufacturing Company and General Aviation Equipment Company. After Pearl Harbor, requirements for both sizes combined rose to eighteen billion for the 2-year period 1942-43. To meet these astronomical requirements a speedier production process was introduced, using a progressive multi-station die developed at Rock Island in the 1930's, and contracts for link production were placed with many different firms. To speed production and break bottlenecks a Metallic Belt Link Industry Integration Committee was formed in the summer of 1942, and by September 1943 the monthly rate of production had reached more than half a billion. Thereafter requirements were reduced with some contracts being terminated outright and others continued at greatly reduced rates. Early in 1945, after the Battle of the Bulge, there was a brief period of rising requirements followed by contract cancellation as the end of the war appeared in view. Total production of metallic links during the 1940-45 period reached close to thirteen billion.

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The United States Army In World War II: Planning Munitions For War
by Constance McLaughlin Green, Harry C. Thomson, and Peter C. Roots
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Chapter VII, Research and Development 1919-40
Small Arms Projects

As far back as 1926 the Secretary of War had tried to hasten the process of standardization of all matériel, but in 1935 the Chief of Staff was still concerned with the problem. At its root lay a philosophy of perfection held by many members of the General Staff, the using arms, and the Ordnance Department itself. General Malin Craig, Chief of Staff from 1935 to 1939, proposed a system of yearly standardization and annual revision that resulted in a directive ordering use in the 1937 program of only standardized equipment, and freezing the design of standardized items from the moment cost estimates were submitted until manufacture was concluded.

But this measure was at best only an alleviation. Difficulties continued. Unequal rates of standardization of closely related items caused great trouble. For example, the 37-mm. infantry gun and carriage was standardized in 1937 but had no ammunition approved for use. Furthermore, unequal rates of standardization of particular components held up acceptance of end items. Of the search for ideal weapons and the delays that search entailed, one observer later wrote: "The best is the enemy of the good."

Not all development projects, to be sure, ran an unduly long course. Modification and redesign of machine guns, begun immediately after World War I, made comparatively rapid progress. Efforts to improve the ballistic and cooling characteristics of the earlier .30-caliber Browning machine guns produced the M1919A4 in 1925, while later collaboration of Ordnance, Air Corps, and Colt Company representatives developed the .30-caliber M2, which could be either fixed or flexible and permitted either right- or left-hand feed. Similarly useful work on mounts went forward.

Still more significant in terms of World War II was the development of the .50-caliber machine gun. In 1930 when the water-cooled .50-caliber Browning machine gun, M1921A, was standardized, the Coast Artillery was satisfied, but Air Corps, Infantry, and Cavalry still lacked what the Chief of Ordnance described as "suitably specialized Brownings." The Air Corps needed lightness, rapid rates of fire, and right- and left-hand belt feeds; tanks required heavy barrel guns with reliable cooling systems.

Neither the using arms nor the Ordnance Department believed it possible to have a single machine gun serve several diverse purposes, but in the two years between 1931 and 1933 Dr. Samuel G. Green of the Ordnance Department succeeded in modifying the Browning to make a single basic gun which, varied by special features for special purposes, could meet requirements for all services. The new model, the .50-caliber M2, was so designed that the operating mechanism was the same for each type of gun. The heavy barrel of the tank gun, the water jacket, sleeve, and 45-inch barrel of the antiaircraft gun, and the lighter parts of the aircraft gun, could each be affixed without modification of the receiver. Here was an outstanding achievement, the benefits of which were to be felt all during World War II; manufacturing, maintenance, and troop training were all eased by this simplification of design.

When the Spanish Civil War provided evidence of the operational value of various items of ordnance, American experts began to question whether the .50-caliber machine gun were not really obsolete both for aircraft and antimechanized use. The using arms therefore ran large-scale tests of the .50-caliber in competition with several types of light automatic cannon. The verdict was in favor of the machine gun.

Chapter XV, Aircraft Armament: Weapons for Air-to-Air Combat

The problems antiaircraft batteries had to deal with in countering the powerful attacks of Axis aircraft were matched, perhaps more than matched, by those the Army Air Forces encountered. Aircraft manufacturers in the United States during the 1930's had been building planes capable of ever-increasing speeds, but as specifications for military craft had slighted the concomitant developments - faster-firing guns, protecting armor, and self-sealing fuel tanks - these netted relatively scant consideration before 1939. Fuel tanks, as an integral part of the plane, were an Air Corps responsibility. Before 1940 the Air Corps had rejected the idea of armored planes, and only when General Henry H. Arnold insisted, after checking the reports of the Battle of Britain, was any attention given to use of protecting armor. Testing suitable materials and preparing specifications then fell to the Ordnance Department because of its experience in ballistics and knowledge of the behavior of plate on armored vehicles under fire. But the major task of the Ordnance Department in developing matériel for the Army Air Forces was to design guns and ammunition for attack.

The Problem of Speed

When President Roosevelt in January 1939 requested of the Congress vast sums of money to produce 50,000 aircraft, only Ordnance experts and a handful of Air Corps officers fully appreciated the need of equipping these planes with very fast firing guns, with more guns per plane, or with both, in order to score hits on enemy planes traveling at new high speeds. General Arnold, to be sure, as early as the summer of 1937 had requested the Ordnance Department to increase the cyclic rate of the .50-caliber aircraft machine gun, and the Springfield Armory and Colt's Patent Fire Arms Company had spent some time on study of the problem. But funds were skimpy, and progress had been proportionately slight. Furthermore, the Air Corps had submitted no list of required military characteristics. Whether to add more guns to a plane to increase its volume of fire was a matter for the Air Corps to decide; the quality of those guns, in keeping with the user's specifications, was up to the Ordnance Department.

American fighters in 1939 carried nothing heavier than .30-caliber and .50-caliber machine guns in multiple mounts on the wings, fuselage, and nose of the plane. Though the standard .50-caliber Browning machine gun M2 of 1939 could fire 600 rounds a minute on a rigid test mount, in some planes that rate was reduced by about 100 rounds a minute, partly because of the aircraft mount's resilience and partly because of the heavy ammunition-belt loads on the gun's feed mechanism. The .30-caliber aircraft gun fired 1,200 rounds a minute, but its muzzle velocity was low and its bullet light. Aircraft guns had to be mounted in confined spaces, so that any redesign or modification must, if possible, retain the external dimensions of the originals in order to minimize modification of the plane to accommodate the new models. Not until late September 1939 did the Air Corps establish the military characteristics wanted in a machine gun of cyclic rate rapid enough to be effective in the shortened "on-target" time of new planes. By then it was clear that what would suffice to hit a target moving at 200 miles an hour would not serve against aircraft flying at 300 to 400 miles an hour.

Higher Cyclic Rates

Accordingly, the Air Corps' major requirement for the new gun was a cyclic rate of at least 1,000 rounds a minute and as much more as other features would permit. The time of bullet flight was to be .7 second for 600 yards and at that range penetrations of .75-inch armor plate must be possible when armor-piercing bullets were used. The over-all length of the gun should be kept within 68 inches and weight as low as was consistent with efficient performance. Other requirements were full automatic fire, controlled by hand and by trigger motor, right-hand and left-hand ammunition feed, adaptability to mounting for either fixed or flexible use, and the least possible trunnion reaction, that is, the lowest possible strain on the shafts upon which the gun was mounted in the plane. Air-cooling the gun with an aerodynamic barrel jacket extending at least 20 inches aft of the muzzle was listed as essential. The Colt's Patent Fire Arms Company, which owned John Browning's patents, undertook design of a gun to meet these requirements, only to have each model tested during the next two years show such serious defects as to be wholly unsatisfactory. In 1940 engineers at the Springfield Armory, by lightening the barrel of the standard M2 machine gun and by substituting double driving springs for a single spring, pushed the cyclic rate up to 800 rounds a minute, but that was still far below the 1,000 rounds a minute the Air Corps wanted.

Increasing the cyclic rate of a gun such as the .50-caliber M2, designed to fire at 650 to 800 rounds per minute, resulted in added stresses upon the barrel and all the moving parts. Even if other components were strengthened enough to avoid excessive breakage, the problem of barrel erosion would remain. The hot gases generated by the explosion of the powder charge softened the bore surface, the chemical composition of the powder attacked the metal, and the high temperature and pressure tended to expand the bore in a very fast-firing gun. Inaccuracy would therefore soon develop unless barrel erosion could be lessened by cooling the barrel, by using a heavier barrel, or by improving the barrel's metallurgy. In February 1942 the Ordnance Department requested NDRC to study the whole problem. NDRC let contracts to some twenty-six companies, universities, and other research institutions, each of which followed out a particular line of investigation. Two and a half years of work, notably that of the Crane Company and the Geophysics Laboratory of the Carnegie Institution, produced a liner of a special alloy which, fastened into the breech end of the barrel, greatly reduced erosion. Further experimentation showed that combining this material at the breech end with chromium plating extending to the muzzle end gave still higher erosion resistance and better general performance.

In the interim, efforts to develop a machine gun of high cyclic rate had continued. Early in 1942 the High Standard Company of New Haven offered a promising design, though the models tested that summer at Aberdeen lacked both the strength and the reliability to be acceptable. Later models, built under a development contract with the Ordnance Department, showed marked improvements but still failed to meet all requirements. Throughout, High Standard worked on the basis of designing a high-speed gun in which changes from the M2 would be kept to a minimum. This came to be a big handicap. Consequently, in August 1943 the Ordnance Department entered into contract with the Frigidaire Division of General Motors Corporation, with the understanding that a gun be developed using the basic mechanism of the M2 aircraft gun but with no restrictions upon the number of changes that might be made. In short, the Ordnance Department abandoned any plan of having parts of the new gun interchangeable with those of the M2. Frigidaire's first model was ready for test in March 1944. It was essentially a new gun; only minor components were interchangeable with the standard M2. Numerous changes were still needed but, by adopting some features of the High Standard experimental models, Frigidaire succeeded by the fall of 1944 in producing a weapon, the T25E3, that had a cyclic rate of 1,250 or more rounds per minute and functioned well enough to warrant fabrication of a hundred for AAF and Navy service test. By the next April the guns that had been carefully service-tested at Wright Field were proving so far superior to the M2 that the Air Forces requested immediate standardization of the new model. The latter then became the .50-caliber aircraft gun M3, and the M2 was reclassified as limited standard.

Development of a machine gun with cyclic rate increased from 800 to 1,200 rounds per minute, at the cost of only a pound in weight and with no significant change from the over-all dimensions of the slower-firing M2, was so impressive an achievement as to merit some particulars. It was accomplished largely by twelve new features. First was a bolt of improved metallurgy and design with holes drilled through to reduce weight. Second was an extractor with a reversible ejector which eased ammunition feeding. Third was the substitution of a pneumatic barrel buffer for the older oil buffer, a change that produced smooth operation regardless of extremes of temperature. Alteration of the curvature of the accelerator resulted in more effective use of the energy of the barrel and barrel extension to accelerate bolt recoil, while a Belleville spring back-plate buffer, using cupped steel washers, accelerated counterrecoil of the bolt. Rigidly mounted breech-lock depressers added to stability of the gun's components during operation. Redesign of the back-plate and of the breech-lock cam strengthened the construction and gave smoother functioning, and an improved firing pin provided about five times as long a life as that of the M2 firing pin. The two features incorporated from the High Standard guns were a special cover assembly to increase ammunition belt-life capacity and split beltholding pawls to improve ammunition feeding. Use of the new erosion-resistant lining for the barrel, moreover, permitted firing long bursts without loss of accuracy or marked drop in velocity.

Unfortunately, few M3's saw action in World War II, as only some 2,400 were completed before September 1945. Yet in the fall of 1944 Ordnance engineers perceived that some desirable proven features of the High Standard and Frigidaire highspeed models could be readily applied to the M2. Among the parts to be used were High Standard's extractor assembly, recoil booster, wide top-cover assembly and split pawls, as well as two parts designed by Frigidaire for the still unperfected T25E3 model. With improved metallurgy, use of a lined barrel, removal of the oil from the oil buffer, and one or two lesser changes, this modified M2 gun, the T36, could fire slightly over 900 rounds a minute. In October 1944 the Air Forces requested 31,336 of these, but rapid progress on the T25E3 limited output to some 8,000.

Encouraging though these developments were, still faster-firing aircraft guns would clearly be advantageous. The Germans, indeed, believed that extremely high cyclic rates would offer the best possible method of combating high-speed craft. Toward the end of the war observers reported on a German development program to introduce aircraft machine guns with cyclic rates well beyond those under development in the United States. The object was to lay down a dense curtain of fire from a very short range. These experimental guns fired short bursts, with firing initiated photoelectrically when the plane was in the proper position. From the American point of view the great drawback of the device was that it did not permit continuous or prolonged fire, a feature the AAF regarded as more important than a single, very fast burst. In 1945 the maximum rate the Ordnance Department set as its goal was 1,500 rounds a minute. Springfield Armory for a time worked on a design of a totally new mechanism suitable for highspeed operation, and Frigidaire designers continued efforts to increase the rate of the M3 to 1,500 rounds per minute, but the war ended before either type had reached the stage of extended testing.

Improvement in the metallic link belts for aircraft machine guns was also needed to make them sturdier and flexible enough to use in restricted spaces such as the plane's tail. The complexity of the problem may be envisaged by study of the accompanying photograph of an installation. A project to improve the link began in the spring of 1940, and, while the Air Corps accepted a modified link early in 1941, search for a design still more serviceable and easier to manufacture continued throughout the war. If, in addition to getting a high degree of strength combined with great flexibility under strain, a lightweight link could be made, the advantages for aircraft guns would be important. Before V-J Day designers tried some twentyeight variations of the standard one-piece link and several two-piece types. Not only design but also materials and heat-treating affected performance in all metallic links. As the light weight of aluminum and plastic suggested substitution of these materials for steel, considerable study of a nylon link went forward, but the effect of extremes of climate upon plastic links and the inelasticity of aluminum prevented development of anything as satisfactory as the steel types used in World War II. In these, lowering the hardness of the steel largely overcame brittleness. Addition of a sprocket to serve as a booster to the feed mechanism also relieved strains.

Higher Muzzle Velocities

Faster-firing guns were not the only answer to the greater speeds of enemy aircraft. Flatter trajectory of fire obtained by higher muzzle velocity was an even surer answer and was sought simultaneously. The NDRC study of hypervelocity noted at the end of the war that, in attacking targets moving in three dimensions, heightening the muzzle velocity of guns by 50 percent would more than triple the number of hits. In any given gun, unless the barrel were lengthened, thereby increasing the weight of the gun, or unless the metallic ammunition components were changed, the only way to increase muzzle velocity without adding to pressures was to use higher-potential powder. But higher-potential powders, like increased cyclic rates, spelled the probability of excessive barrel erosion. This could be avoided only by keeping the temperature of powder combustion low. Extensive experimentation, largely at Frankford Arsenal, produced .50-caliber ammunition with muzzle velocity heightened from 2,700 to 2,880 feet per second, but even with lined barrels the danger of "keyholing" after firing relatively few rounds forbade more powerful charges. As the interior surface of the barrel wore, the projectile tended to deform so that it lost velocity and tumbled in flight, and upon impact made a keyhole-shaped mark. If the barrel became excessively hot the bullet might even break through the wall of the barrel. At the very end of the war tests at the Ordnance research and development center indicated that a newly developed lighter-weight cartridge, the armor-piercing-incendiary T49, using a single-base powder, would give muzzle velocity of over 3,400 feet per second, but the erosion properties of the T49 were still a drawback.

The German point of view on high muzzle velocities in aircraft weapons offers a contrast to the American concept: Investigation of German small arms development and production revealed that, as concerns automatic weapon design, the attainment of a high cyclic rate appeared to be a primary consideration. This was particularly true in the case of automatic weapons designed for aircraft use. Apparently German authorities believed that a relatively low muzzle velocity was acceptable if a high rate of fire could be obtained. High velocities required larger and heavier rounds with a consequent reduction of cyclic rate . . .

Training Devices for Bettering Marksmanship

Use of power-driven turrets developed by the Air Forces to enable the aircraft gunner to locate his quarry quickly and track him accurately was another means of dealing with the problem of hitting a target moving at high speed. There remained the human factor in marksmanship. Whatever the perfection of gun mechanisms, Army and Army Air Forces both knew that soldiers must be well trained in their use; few weapons were highly effective in the hands of the inept or inexperienced. Where speed of hand and quickness of eye were so vital as to the aircraft gunner, his training became of more than usual importance. Skeet shooting, firing at a towed airborne sleeve or "drone," and shooting a camera gun were used in the early part of the war, but the shortcomings of those methods of training were so obvious that the Air Forces in September 1942 requested a conference with the Ordnance Department to discuss ways of improving upon them. The Air Forces proposed that the Ordnance Department develop a projectile that would disintegrate upon impact without harm to the target or its crew, but a projectile with ballistics similar under training conditions to those of the service ammunition under combat conditions. The Air Forces, agreeing that a suitably armored target plane would be essential to successful use of a frangible cartridge, undertook to develop an armored plane. Two months later the Air Forces changed its mind about the armored target plane and informed the Ordnance Department that unless a bullet could be made that would shatter against an unarmored craft, the whole project must be abandoned. The Ordnance Department dropped it. Research men of NDRC later charged that "one or two willful men in the Ordnance Department nearly stopped the development altogether." The Ordnance staff averred that the Air Forces had tied its hands.

At this point, one or two Air officers, convinced of the value of the idea, persuaded the Air Forces to turn the problem over to NDRC and approve a research contract with Duke University. Experiments were to be confined to work upon a .30-caliber bullet because, though .30-caliber machine guns were ineffective in combat against the armor plate of World War II planes, the firing characteristics were nearly identical with those of the more powerful .50-caliber, and the smaller-caliber ammunition was cheaper. In the course of the next year men at Duke and NRDC came up with a 90-grain bullet of powdered lead bonded with bakelite that, fired from a modified .30-caliber aircraft machine gun, at a distance of 50 yards disintegrated against a quarter inch plate of dural placed normal to the line of fire, or, if the bullet perforated the plate, caused little or no damage. This achievement was encouraging, though it still did not meet the Army Air Forces specifications. The Air Forces then requested the Ordnance Department to continue the development, but Maj. Cameron Fairchild, AAF, Professor Paul Gross and associates at Duke, members of NDRC, and the Bakelite Corporation, who had been the chief proponents of the program thus far, largely saw it through.

The technical difficulties were various. Beside making a frangible bullet with the proper ballistics and adapting the machine gun to firing ammunition with reduced powder charge, a plane had to be built, armored enough to be safe and yet able to fly. A hit indicator system had to be devised and a plan worked out for vectorial scaling of bomber and fighter velocities, for the bullet muzzle velocity, and for the ring sight size. The bullet T44, finally produced in some quantities and used at several training fields toward the end of the war, was slightly heavier than the first experimental type. The machine gun was satisfactorily modified and the scaling problem solved. The Air Forces did build an armored plane upon which hits were scored automatically by electrically amplifying the vibration caused by the bullet's impact and thus flashing a light on the nose of the plane. Yet in spite of these successful developments, only a small fraction of bullets manufactured were fired. After the war Air Forces psychologists concluded that trainees were prone to get false ideas of aiming and firing because the bullet simulated too much. The frangible cartridge was then declared limited standard.

Tracer Ammunition for Bettering Marksmanship

As an aid to accurate fire, tracer ammunition had long been held in high regard by the Air Corps. In 1924 an improved .30-caliber tracer cartridge was standardized as the M1, the combat characteristics of which remained unchanged until Pearl Harbor. But after the Battle of Britain in 1940 the British, though praising tracer as a medium of fire control, wanted a controlled length of trace and, in order to minimize the blinding effect upon the gunner, a delay of 150 yards before the brightburning powder ignited. Satisfactory types were developed in the course of the next two years, but Obsoletion of .30-caliber machine guns for Army aircraft resulted in limiting .30-caliber tracer to ground use and, in small quantities, to use by the naval air forces. Caliber .50 tracer, on the other hand, mounted in importance as the war progressed. A type standardized in 1931 as the M1 formed the basis of the .50-caliber tracer most widely used by the Air Forces during the first two years of the war, though improvements were made in the original bullet by changing tracer and igniter mixtures, by increasing velocity 330 feet per second, and by developing clad-steel bullet jackets. Frankford Arsenal modifications of the M1 produced ammunition with a controlled bright trace of 550 plus or minus 50 yards, and later a type, standardized as the M10, which not only eliminated risk of blinding the gunner and gave a sufficient glow during the first moments of flight to permit him to retain trace image but also had ample intensity to enable him in daylight firing to follow the trace for the duration of the ignition. Thus, the M10 could be used in both night and day combat. It had, moreover, the advantage of longer life with less deterioration in storage than several other types of tracer ammunition.

Another variation of the M1 tracer was developed between 1942 and 1944, a socalled headlight tracer, which gave a frontal visibility three times as bright as the M1. Initial reports from active theatres indicated that the psychological effect upon enemy pilots gave this bright-burning tracer particular value. The Tenth Air Force in December 1944 stated: "Preliminary reports indicated that they (caliber .50 headlight tracer cartridges) make adjustment of fire easier. Enemy pilots seem to be less aggressive and show a tendency to break off combat at longer range than with standard ammunition . . . ." And the Commanding General, Strategic Air Forces in Europe, cabled: "Brilliant tracer indicates enemy fighter to other gunners in formation, which enables our planes to spot enemy aircraft more effectively at greater distances. . . . (This) ammunition is an important factor in breaking up enemy fighter attacks at extreme ranges." Furthermore, pilots at that time believed that this tracer used in ground strafing disturbed flak tower operations. It was therefore standardized as the caliber .50 headlight tracer M21. Only after the war did the Air Forces conclude that enemy pilots had been less easily scared by this ammunition than first reports stated. The M21 was then dropped.

The Problem of Effective Striking Power
Incendiary Ammunition

Rapidity of fire, flat trajectory, and accuracy of aim might solve the problem of scoring hits against enemy planes flying at high speeds, but if shots failed to disable the plane or crew, the effect of accuracy was lost. Greater striking power could be achieved by increasing machine gun muzzle velocities, by using air cannon that fired bigger projectiles, or by employing rockets. The threat of encountering enemy armor plate capable of withstanding .50- caliber machine gun fire did not actually materialize in World War II, but bullet penetration of the plane's armor did not necessarily knock out aircraft. Enemy use of self-sealing fuel tanks necessitated development of effective incendiary ammunition.

A .30-caliber- incendiary had been used in World War I but, because of difficulties in manufacture, was later discarded for tracer. When in 1939 and 1940 tests of incendiary characteristics of the tracer showed it to be unsatisfactory, search for suitable incendiary ammunition began again. The Chief of Cavalry and Chief of the Air Corps in July 1940 submitted requirements for incendiary .30-caliber and .50-caliber rounds that upon striking would ignite a gasoline or oil tank or pipelines from the tank. Time of flight was to be approximately that of standard ammunition and the center of impact was to be within twelve inches of the center of impact of standard Air Corps ammunition. Fortunately the British had made some progress with the problem. During the Battle of Britain in the fall of 1940 they had employed a .303-caliber incendiary cartridge that was effective against German bombers. But, like the World War I incendiary, its design was so complex that simplification was essential for quantity manufacture. Frankford Arsenal, assigned the task of redesigning the British .303 both to adapt it to mass production and to convert it to .30-caliber, succeeded in evolving a satisfactory bullet and cartridge by September 1941. This became the .30- caliber incendiary M1 and was issued linked in the ratio of two armor-piercing-two incendiary-one tracer, until in 1943 the Army Air Forces discarded .30-caliber machine guns altogether.

More urgently needed was an effective .50-caliber incendiary. The first acceptable design was the work of the Remington Arms Company, whose staff had already had considerable experience in work on Swiss patents for incendiary ammunition. The Remington development was based upon the British .303 B Mark VI Z and was adopted in September 1941. The bullet was a flat-base type with lead base closure and steel body and was charged with 35 grains of incendiary mixture, 50 percent magnesium alloy and 50 percent barium nitrate. A few months later Frankford produced a type of .50-caliber boattailed bullet that equalled Remington's in performance and proved better adapted to mass production. The Frankford design was standardized and the Remington became the Caliber .50 Incendiary M1 Alternate.

By 1942 flyers had come to regard some type of incendiary as indispensable for air combat. "These pilots, who are in daily conflict with the enemy, swear by the effectiveness of the incendiary ammunition and would as soon go up without their machine guns as without this type of ammunition." But the M1 incendiary did not serve every purpose. In the spring of 1943 the air forces were suffering heavy losses of B-17's in daylight bombing operations over Europe, partly because the M1 incendiary, though excellent against enemy fighters approaching from most angles, was ineffective against frontal attack. The protection afforded by the engine of the enemy craft served to exhaust both the incendiary and the penetration energy of the projectile before it got to the fuel tank. Ordnance small arms ammunition specialists consequently suggested use of the M8 armor-piercing-incendiary developed for antiaircraft defense. The M8, when manufactured in relatively small quantities, proved more efficient than either armor-piercing or standard incendiary rounds, but, when manufactured by mass production methods with the types of powder then available, retention of its high velocity became impossible. Inasmuch as armor-piercing-incendiary with less velocity lost most of its penetrating and its incendiary properties, the Ordnance Department recommended that until something better could be perfected the M1 incendiary continue to be used for general air combat and straight armorpiercing for ground strafing. The something better than either standard incendiaries or the M10 tracer emerged in the spring of 1944 in the T28 armor-piercing incendiary tracer standardized in March 1945 as the M20. Air Forces theatre commanders were authorized to request such quantities as they saw fit.

Meanwhile, in the winter of 1943-44, increasing German employment of jetpropelled aircraft burning kerosene created the need for .50-caliber ammunition capable of igniting aviation kerosene. Half a dozen different Ordnance plants worked on the problem. The Des Moines Ordnance Plant produced the most satisfactory model, a 500-grain bullet containing 90 grains of an incendiary mixture composed of 50 percent magnesium aluminum alloy, 40 percent barium nitrate and 10 percent potassium perchlorate. A single-base powder was used that was found to be superior to double-base powder for firing extended bursts. Quantities of the Des Moines cartridge, listed as the T48, were shipped to the theatres in the winter of 1944-45 and proved so effective that in May 1945 the T48 bullet was standardized as the .50-caliber M23 and the round as incendiary cartridge M23. A report of June 1945 from Headquarters, U.S. Strategic Air Forces in Europe, was enthusiastic: "Most pilots stated that aircraft burst into flames more readily when hit with this type ammunition in contrast to armor-piercing incendiary ammunition. Many enemy aircraft burned after having been hit only two or three times. . . . One pilot destroyed 10 aircraft on a single mission by firing short bursts." This testimony notwithstanding, design of incendiary and armor-piercing incendiary ammunition remained at the end of the war a problem requiring much additional study.

The Problem of Functioning at High Altitude

Study of the effects of severe cold on gun steels and oils was part of the mission of the WinterDetachment sent to Camp Shilo in Manitoba in December 1942. All air ordnance tested there performed satisfactorily if lubricated with suitably thin oils. Nevertheless, inasmuch as improved oil buffer assemblies in machine guns would minimize oil leakage at high temperatures and congealing at low, during 1943 Springfield Armory experimented with use of new synthetic packings, new finishes, and design modifications, until the Frigidaire Division of the General Motors Corporation evolved the pneumatic type buffer that used no oil at all. Two helical springs absorbed the recoil and functioned so well in tests in the fall of 1944 that this mechanical buffer was incorporated as a feature of the M3 aircraft machine gun. Not only did the air-and-spring type buffer dispense with the use of oils, the spring action allowed markedly increased rates of fire. Furthermore, in the modified M2 aircraft gun, engineers found it possible to use the oil buffer without oil.

Experience taught the Air Forces that the .50-caliber machine gun was an eminently reliable weapon for the combat conditions of World War IL The 1,453,829 .50-caliber aircraft guns produced testifies to their usefulness. Nevertheless, by V-J Day indications pointed to the probability that more powerful, bigger guns would be employed increasingly as aircraft structures became heavier and stronger and their speeds still greater.

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Manual Excerpts

The following are excerpts from Army manuals that contain dimensional information. I've also included any that I thought had historical value regarding time period for changes in the gun, and part numbers for identification of correct parts. Note that any instructions are obsolete, do not use for rebuilding a working gun.

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TB ORD 366 - TO 11W3-1-6 - Rebuild Standards For Small Arms Materiel - Department Of The Army Technical Bulletin - Sept 15 1953
This bulletin, together with TB 9-9125-1 26 June 1953, supersedes TB ORD 366, 9 August 1949, including C 1, 18 October 1949
This bulletin is correct to 6 May 1953
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  • Marking of rebuilt weapons.
  • All rebuilt machine guns, pistols, rifles (including automatic rifles), and carbines will be stamped with the initials of the rebuilding establishment in the United States. Weapons rebuilt by oversea depot maintenance shops will not be stamped. On machine guns, the initials will be stamped on the right-hand side plate, directly to the left of the serial number. On pistols and Browning automatic rifles, the initials will be stamped as close as possible to the serial number. On all rifles (except the Browning automatic rifle) and carbines, the initials will be stamped on the left side of the stock, between the hand grip and the butt plate. If the weapon is subsequently rebuilt at another establishment, the new identifying initials will be placed directly below those preceding. If the weapon is rebuilt at the same establishment as before, new initials need not be added. The establishments and the initials to be used are as follows:
    Augusta Arsenal - AA
    Benicia Arsenal - BA
    Mt. Ranier Ordnance Depot - MR
    Raritan Arsenal - RA
    Red River Arsenal - RRA
    Rock Island Arsenal - RIA
    Springfield Armory - SA
  • Final finish.
  • All components, except springs, will be finished with type II, class B phosphate finish in accordance with current requirements. Exterior springs must be finished. Inner springs one-eighth inch or under in diameter must not be finished. All other springs may or may not be finished, depending on circumstances.
  • Mounts.
  • (5) Replace missing or obliterated serial number on mount. Such serial numbers may be obtained from Chief of Ordnance, Washington 25, D. C., ATTN: ORDFM.
  • (6) Remove mount name plate and stamp the mount serial number and manufacturing data in the same location. Dispose of name plate in accordance with SR 735-150-1.
  • Receiver group, general.
  • All heavy barrel and water-cooled guns must have modified retracting slide group assembly D6573953.
  • All heavy barrel, fixed guns must be equipped with side plate trigger assembly C5546031.
  • Solenoids must be packed with heavy barrel, turret type guns.
  • HB and turret type guns are to have a 3/8-inch hole in right side plate for new type barrel locking spring.
  • Side plate assemblies.
  • (2) Trigger motor (and RSG) slots should have a 60-degree angle at the rear end of the small slot and the front end of the large slot (fig. 76) A 0.020-inch flat should be on the outside forward edge of the large slot and on the outside rear edge of the small slot. There should be no sharp corners. Check to see that the solenoid or side plate trigger can be attached.
  • (5) Belt holding pawl brackets must have two holes for the two belt holding pawl springs as shown in figure 77.
  • (6) Remove the rear extension of early design right-hand belt holding pawl brackets. An overall length of 6 9/64 inches (fig. 78) should be maintained. This applies only to aircraft guns.
  • (7) Belt feed lever clearance cut on top of right-hand side plate must have the following dimensions: 4.25 +0.03-inch long, 0.17 +0.01-inch deep, and 1-inch radius turnout as shown in figure 79.
  • (8) Beveled edge directly over feedway must be carried around rear corner as shown in figure 80. This corner must have a 1/4- to 5/16-inch radius.
  • Top plate group.
  • (2) Trigger bar B6257592 (rev 5 and above) (fig. 81) must be used in all aircraft and turret type guns. Although this trigger bar can be used in the flexible ground gun, stocks of trigger bar B6008944 will be used conserving the supply of trigger bar B6257592 for aircraft and turret type guns.
  • (3) All aircraft and heavy barrel, flexible and turret type guns must have adjustable trigger bar stop assemblies B7265212 (figs. 82 and 83). Remove approximately one-eighth inch from rear trigger bar stop to assure that it does not project below the adjustable trigger bar stop.
  • (4) All aircraft and heavy barrel, flexible and turret type guns should have trigger bar pin assembly B7310075 (figs. 84 and 85) or B7313106.
  • (7) All aircraft guns should have the serial number on the top plate (fig. 86) as well as the side plate. In stamping numbers, do not deform the top plate. Numbers should be uniform and should be filled in with white graduation filler.
  • Bottom plate group.
  • (2) Bottom of plate should be spot-faced for the breech lock cam bolt nut (1 5/8-inch diam).
  • (4) Diameter of the rear mounting holes will be 0.440 to 0.443 inch for aircraft guns. Diameter of rear mounting holes for all other guns will be 0.440 to 0.445 inch.
  • (5) Inside width of mounting lugs will be 1.499 to 1.503 inches.
  • (6) Outside width of mounting lugs will be 2.296 to 2.302 inches.
  • Belt holding pawl pin. Pin must be sufficiently loose to be removed by hand. All aircraft guns must have belt holding pawl pin assembly B7160030 (fig. 77) or B7313328. Install belt holding pawl pin assembly B7162872 in all other weapons.
  • Link stripper. Link stripper must be loose; however, the bottom of the lower prong of the stripper must not lift above the rib on the surface of the trunnion block.
  • Cover group assembly.
  • (1) Detent should hold cover open and operate without binding. Detent guide should not be unscrewed to the extent that it bottoms against the barrel support or water jacket, causing cover to bind when opened.
  • (2) If the cover detent is disassembled, omit the cotter pin on heavy barrel and water-cooled guns.
  • (3) Do not squeeze lugs in below 1.498 to 1.500 inches. A small amount of play is permissible between the cover and trunnion lugs. However, the cover is not to bind at this point.
  • (4) Clearance between the cover latch and notch in the top plate should not exceed 0.010 inch (fig. 88). Cover must bottom on each side plate.
  • (5) The cotter pin in the belt feed lever stud must not interfere with the ammunition and must be of the proper size (3/32 X 3/4) to assure that the lever does not drop down on the stud. Use belt feed lever retaining pin A7312970, if available.
  • (6) The belt feed lever must be of the latest design, which can be identified by a 3/16-inch star stamped thereon, as shown in figure 89, and must check with location of ends gage 6511124.
  • (10) All guns must contain belt feed slide assembly B6261110 (fig. 90). Belt feed lever slot must measure not over 0.309 inch maximum.
  • (13) Belt feed pawl arm will conform with belt feed pawl arm gage 7319902.
  • (15) The belt feed lever should not contact the ends of the "T" slot in the cover. The length of the "T" slot should be 1.766+0.010 inch (fig. 91). Covers which have been improperly modified may exceed these dimensions; if so, they are usable, if the belt feed lever cams into the bolt track when closing the cover.
  • (16) Omit short round stop B7312529.
  • (17) Only belt feed pawl spring with oblong coil on large end will be used. This change was made effective in manufacture in July 1942. The old type may be disposed of as unserviceable.
  • (18) Serviceable covers {without weapon serial number) which are removed for finishing are lo be identified by stamping weapon serial number on the inside of cover.
  • Barrel jacket group (aircraft guns).
  • (1) Outside diameter will be 1.860 to 1.880 inches.
  • (2) There will be no looseness of breech bearing in the trunnion. There also will be no looseness of the barrel jacket in the breech bearing.
  • (3) Inside diameter of the front bearing will be 1.156 to 1.161 inches.
  • Barrel support (heavy barrel guns).
  • (1) The maximum diameter of the barrel bearing surface is 2.330 inches.
  • (2) It must fit tightly on the trunnion.
  • (3) Remove all barrel support adapters and Edgewater adapters and replace them, with barrel supports.
  • Water jackets (water-cooled guns).
  • (1) The jacket must be free of leaks and must be able to withstand a minimum of 30 pounds internal hydraulic pressure, sustained for a period of 3 minutes.
  • (4) Steam tube must be free to slide on supports.
    Note. Some guns were made with a stationary steam tube assembly These guns can be identified by the absence of brass steam tube support in the front end of the jacket.
  • Barrel and barrel extension group.
  • (1) Barrels on hand which have been removed from guns, should be inspected for serviceability in accordance with paragraph 5. If they appear serviceable and have sharp and distinct lands and pits not exceeding one-half inch, they should he boregaged. using breech bore gage 7319900. Breech bore reading is not to exceed the fifth graduation of the gage for unlined steel barrels. Bullet seats may be checked with gage conforming to drawing C5564348. The gage may be manufactured locally. Used barrels of guns other than aircraft are suitable for training purposes, if the gage does not enter past the thirteenth graduation. Barrels meeting the above specifications are to be set aside and disposition instructions requested from nearest distribution depot. They should be checked to insure that they have the modified bullet seat and that there are sufficient threads to allow proper head spacing.
  • (4) Remove the rear 14 inches from unserviceable barrel assemblies containing Stellite liners, retain in shop until a sizeable quantity has accumulated, and ship to Springfield Armory, Springfield, Massachusetts, for salvage ol Stellite liners.
  • Barrel extension group.
  • (1) Barrel locking spring must not bind against the side plate when head spacing the gun. Check for wear on the spring detent and be sure that the spring has sufficient tension. Heavy barrel and heavy barrel turret type guns must be modified and contain barrel locking spring B7265115.
  • Oil buffer group assembly.
  • (4) Oil buffer tube lock assembly C5645325 (fig. 93) must be installed in all guns.
  • (1) Oil will not be used in heavy barrel guns. Buffer filler screw should be retained in all guns. "H.B." will be stamped on the bottom of the buffer tube for identification purposes. Omit the following parts shown in figure 94.
    A9279 - PACKING, oil buffer gland (early mfr)
    A9297 - RING, oil buffer gland packing (early mfr)
    A5009360 - SCREW, oil buffer relief valve
    A9290 - SPRING, compression, S, 0.047 diam stk, 0.420 OD, 7 coils (oil buffer packing gland) (early mfr)
    A5009393 - SPRING, compression, S, 0.034 diam stk, 0.208 OD, 5 1/2 coils (oil buffer relief valve)
    A5009528 - VALVE, relief, oil buffer
  • (6) All aircraft and water-cooled guns using oil filled buffers will have the latest type filler screw assembly B6147888 with copper washer. To utilize existing stocks of the old type screws now in storage, screw A5009361 will be used, when available, in guns not employing oil filled buffers. Screw B6147888 should not be used as the copper washer is usually deformed. Bolt assemblies which are serviceable, with the exception of the recoil plates, will he returned to Rock Island Arsenal, Rock Island. Illinois, for repair when a sufficient amount has accumulated.
  • (7) New type packing A5153162, spring A5153163, and washer A5153161 must be used in all guns with oil filled buffers.
  • Bolt group assembly.
  • (1} There must be no sharp corners on any surface of the bolt.
  • (2) Extractor pivot hole must not exceed 0.3640 inch.
  • (5) Dimension from top of the extractor stop pin to the bottom of the bolt guide rib will be 0.744 to 0.751 inch.
  • (6) Depth of the "T" slot must be within 0.193 to 0.201 inch.
  • (7) Dimension from the front inside face of the "T" slot lips to the face of the bolt must be within 0.084 to 0.888 inch. (possible typo, 0.088?)
  • (8) Fillets in the "T" slot must be 0.01 radius +0.01 inch in the corners.
  • (10) Replace all sear slides A13595 with sear slides A5351120.
  • Back plate assembly.
  • a. Adjusting screw must be tight. Screw must not protrude more than one thread (0.153 in.) beyond the rear of the buffer tube and must not be in below flush level with the buffer tube as shown in figure 101. Torque in tightening the adjusting screw will be 20 to 40 foot-pounds. Plunger must be in locking notch in the back piate buffer tube.
  • b. Back plate must fit tightly but must not bind, preventing removal by hand.
  • c. Buffer plate will protrude approximately three-sixteenths of an inch from the back plate.
  • e. Back plate with horizontal buffer assembly C5564311 (fig. 102) is standard for aircraft and heavy barrel, fixed and turret type guns.
  • f. Back plate with horizontal buffer assembly D6535476 (fig. 103) is standard for water-cooled gun.
  • g. Spade grip back plate assembly D6535477 (fig. 104) is standard for heavy barrel flexible gun.
  • A. Locking pin 7312517 (fig. 102) may be used to retain back plate latch lock clevis pin A5013581 (fig. 104).

blank

The following is in progress, mount part numbers and some text details are incomplete.

*****************************************
TM 9-1225, ORDNANCE MAINTENANCE
BROWNING MACHINE GUN. CAL. .50,
M2 ALL TYPES, AND GROUND MOUNTS
October 23rd 1944
*****************************************

This Technical Manual supersedes:
TM 9-1225, dated 15 April 1943;
Change No. 1, dated 1 July 1943; Changes No. 2, dated 5 September 1943; Changes No. 3, dated 15 October 1943; and Changes No. 4, dated 6 April 1944.
This manual also supersedes:
TB 9-1225-21, dated 20 June 1944; TB 9-1225-22, dated 21 June 1944; and TB 9-1225-23, dated 25 August 1944.
 
SECTION I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.
XIII.
XIV.
XV.
XVI.
XVII.
XVIII.
XIX.
INDEX
Introduction
General description
Inspection
Tools
General maintenance
Back plate group
Bolt and driving spring group
Oil buffer group
Barrel and barrel extension group
Cover group
Casing group
Water chest, cal. .50, M3
Ammunition chest, cal. .50, M2
Machine gun tripod mount, cal. .50, M3 and antiaircraft elevator cradle, cal. .50, M1
Machine gun antiaircraft mount, cal. .50, M2A1
Machine gun antiaircraft mount, cal. .50, M3
Machine gun antiaircraft mount, cal. .50, M63
Accessories
References
 
*****************************************
  • GENERAL DESCRIPTION - Section II
  • Page 10 text
  • HB Barrel Support Adapter for Mount M2A1 - C121036
  • Water Chest, Cal. .50, M3, 1-C-3506 w / Hose - Figure 9 - Page 11 - RA PD 86099
  • title p/n only
  • Ammunition Chest, Cal. .50, M2, 4-C-1138-40 - Figure 10 - Page 11 - RA PD 86100
  • title p/n only
  • Link-delinking Machine, Cal. .50, M7, 1-M-72-625 - Figure 11 - Page 12 - RA PD 49068
  • title p/n only
  • Hand Linker-Delinker, Cal. .50, M12, 41-L-1604 - Figure 12 - Page 12 - RA PD 91905
  • title p/n only
  • Page 24 text
  • Water Chest, Cal. .50, M3, A037-03-00014
  • Ammunition Chest, Cal. .50, M2, A037-6528399
  • TOOLS - Section IV
  • Breech Bore Gage, Cal. .50, M1, 41-G-30 - Figure 20 - Page 27 - RA PD 50971
  • title p/n only
  • Breech Bore Gage, Cal. .50, 41-G-29-50 - Figure 21 - Page 27 - RA PD 22709
  • title p/n only
  • Special Tools and Gages - Figure 22 - Page 28 - RA PD 91902
  • A - REFLECTOR, BARREL, CAL. .50 - 41-R-2331-25
  • B - GAGE, HEADSPACE AND TIMING, CAL. .50 - 41-G-201-150
  • C - WRENCH, HOLDING, BARREL - 4l-W-530
  • D - WRENCH, ADJUSTING, PACKING RING - 41-W-3242-500
  • E - GAGE, FIRING PIN HOLE, CAL. .50 - 41-G-182-200
  • Headspace and Timing Gages Comprising Assembly 41-G-201-175 - Figure 23 - Page 29 - RA PD 65581
  • HEADSPACE GAGE, CAL. .50 (A351211)
  • TIMING GAGE, CAL. .50 (A351213)
  • TIMING GAGE, CAL. .50 (A351214)
  • Combination Wrench, Cal. .50, M2, 41-W-3249-850 - Figure 24 - Page 29 - RA PD 50973
  • title p/n only
  • Machine Gun Wrench, Cal. .50, M2, 41-W-867-849 - Figure 25 - Page 30 - RA PD 26995
  • title p/n only
  • Combination Wrench, Cal. .50, M2, 41-W-867-808 - Figure 26 - Page 30 - RA PD 90816
  • title p/n only
  • Firing Pin Spring Removing Tool 41-T-3098 - Head Partly Cut Away To Show Construction - Figure 27 - Page 31 - RA PD 68443
  • title p/n only
  • GENERAL MAINTENANCE - Section V
  • Page 35 text
  • Packing, Oil Buffer, Leather (old types) - A9279 or A9279A
  • Page 36 text
  • Packing, Oil Buffer, Asbestos, Synthetic Rubber, and Graphite (new type) - A153162
  • BACK PLATE GROUP - Section VI
  • Back Plate With Horizontal Buffer Assembly - Exploded View - Figure 28 - Page 39 - RA PD 91822
  • A - PIECE, FILLER, BACK PLATE - A152753
  • B - PIN, BACK PLATE FILLER PIECE - A9275
  • C - PLATE, BACK - D35276
  • D - PIN, LOWER FILLER PIECE - A152854
  • E - PIN, BACK PLATE LATCH - A9275
  • F - PIN, COTTER (1/16" X 7/16") - 137130
  • G - SPRING, BACK PLATE LATCH - A9356
  • H - LATCH, BACK PLATE - B8949
  • I - LOCK, BACK PLATE LATCH - B147464
  • J - SPRING, BACK PLATE LATCH LOCK - B243607
  • K - PIECE, FILLER, LOWER - A152750
  • L - SCREW, ADJUSTING - A152834
  • M - SPRING, ADJUSTING SCREW PLUNGER - A9300
  • N - PLUNGER, ADJUSTING SCREW - A152839
  • O - DISK, BUFFER (22 USED) - A152835
  • P - PLATE, BUFFER - A152869
  • Q - PIN, BACK PLATE LATCH LOCK - A13581
  • Back Plate With Horizontal Buffer Assembly With Trigger Group (Water - cooled Guns) - Partly Exploded View - Figure 29 - Page 40 - RA PD 91823
  • PIN, TRIGGER - A9275
  • SAFETY, TRIGGER - B147511
  • SPRING, TRIGGER SAFETY - A152896
  • SCREW, TRIGGER SAFETY (2) - A152897
  • SPRING, TRIGGER - A9352
  • TRIGGER - B8918
  • SPACER, BACK PLATE TRIGGER - A13583
  • Spade Grip Back Plate Assembly With Bolt Latch Release {Heavy - barrel Guns) - Exploded View - Figure 31 - Page 41 - RA PD 91824
  • A - PIN, BACK PLATE LATCH (AND TRIGGER) - A9275
  • B - LATCH, BACK PLATE - B8949
  • C - SPRING, BACK PLATE LATCH - A9356
  • D - SPRING, TRIGGER (AND BOLT LATCH RELEASE} - A9352
  • E - PLATE, BACK - D35475
  • F - FRAME, HANDLE, UPPER - B8937
  • C - SCREW, HANDLE TUBE - A9394
  • H - FERRULE, HANDLE GRIP - A9517
  • I - TRIGGER - B8918
  • J - RELEASE, BOLT LATCH - C4071
  • K - PLATE, BUFFER A152869
  • L - DISK, BUFFER A152835
  • M - PLUNGER, ADJUSTING SCREW - A152839
  • N - SPRING, ADJUSTING SCREW PLUNGER - A9300
  • O - SCREW, ADJUSTING - A152834
  • P - GRIP, HANDLE (2) - A9265
  • Q - PIN, BACK PLATE LATCH LOCK - A13581
  • R - PIN, COTTER (1/16" X 7/16") - 137130
  • S - LOCK, BACK PLATE LATCH - B147464
  • T - SLEEVE, BUFFER TUBE - B8926
  • U - SPRING, BACK PLATE LATCH LOCK - A152875
  • V - FRAME, HANDLE, LOWER - B8936
  • Vertical Buffer Back Plate Assembly - Exploded View - Figure 32 - Page 42 - RA PD 91825
  • SCREW, ADJUSTING - A9833
  • PLUNGER, ADJUSTING SCREW - A9278
  • SPRING, ADJUSTING SCREW PLUNGER - A9300
  • DISK, BUFFER (15 USED) - A9374
  • BUFFER, UPPER - A9776
  • BUFFER, LOWER - A9775
  • PLATE, BACK - C8469
  • FINGER, OIL BUFFER INDEX - B17166
  • PIN, OIL BUFFER INDEX FINGER - A9791
  • PIN, STOP, OIL BUFFER INDEX FINGER - A9790
  • KEY, OIL BUFFER INDEX - A9785
  • SPRING, OIL BUFFER INDEX KEY - A9803
  • LATCH, BACK PLATE - B8949
  • PIN, BACK PLATE LATCH - A9275
  • SPRING, BACK PLATE LATCH - A9356
  • LOCK, BACK PLATE LATCH - A13575
  • PIN, BACK PLATE LATCH LOCK - A13574
  • PLUNGER, BACK PLATE LOCK - A13577
  • SPRING, BACK PLATE LATCH LOCK - A13576
  • Page 46 text, parts to convert fixed back plate to flexible, for truck mounts
  • PLATE, BACK, SPADE GRIP CONVERSION GROUP ASSEMBLY - D35541
  • BAR, TRIGGER - B8944 OR B257592
  • PIN, TRIGGER BAR, ASSEMBLY - B8683
  • Spade Grip Back Plate Conversion Group Assembly - Exploded View - Figure 34 - Page 47 - RA PD 91901
  • FRAME, HANDLE, UPPER - B8937
  • FRAME, HANDLE, LOWER - B8936
  • PIN, HANDLE FRAME (4) - A152854 (SECURE WITH PIN, LOCKING - A7312517, OR PIN, COTTER, SPLIT, S., 1/16" X 7/16" - 137130)
  • GRIP, HANDLE, ASSEMBLY - B8765
  • TUBE, HANDLE - A9369
  • SCREW, HANDLE TUBE (4) (STAKE IN PLACE) A9394
  • TRIGGER - A8918
  • SPRING, TRIGGER - A9352
  • SPACER, BACK PLATE TRlGGER - A13583
  • SAFETY, TRIGGER - B147511
  • SPRING, TRIGGER SAFETY - A152896
  • SCREW, TRIGGER SAFETY (2) - A152897 (STAKE TO BACK PLATE)
  • Page 48 text, parts to convert flexible back plate to fixed, for Machine Gun Antiaircraft Mount, Cal. .50, M3
  • PIECE, FILLER, LOWER - A152750
  • PIN, LOWER FILLER PIECE - A152854
  • PIN, COTTER (1/16" X 7/16") - 137130
  • Page 44-48 text
  • Usages, as issued:
  • Heavy-barrel fixed:
  • Antiaircraft Mount M3, and Antiaircraft Mount M2A1 (M2A1 is used with barrel support adapter C121036, a Rock Island Arsenal direct requisition listed in the addendum of SNL A-39)
  • Heavy-barrel flexible:
  • Ring-type Truck Mounts such as M32, and Antiaircraft Elevator Cradle Cal. .50, M1
  • Water-cooled flexible:
  • Pedestal Mounts M43, M43A1, and M46, convert back plate D35476 (with trigger and trigger safety but no spade grips) with spade grip conversion group D7160981
  • Page 49 text
  • Convert a aircraft, basic, fixed (with back plate C64311, no trigger, trigger safety, or spade grips) to flexible with spade grip back plate conversion group assembly D35541
  • BOLT AND DRIVING SPRING GROUP - Section VII
  • Extractor Assembly - Exploded View - Figure 36 - Page 52 - RA PD 91826
  • SPRING, EJECTOR - A9523
  • EJECTOR - B9732
  • PIN, EJECTOR - A9273
  • EXTRACTOR - C4065
  • Firing Pin Extension Assembly - Exploded View - Figure 42 - Page 55 - RA PD 91827
  • EXTENSION, FIRING PIN - B8946
  • SPRING, FIRING PIN - A9353
  • PIN, STOP, FIRING PIN SPRING - A9382
  • Page 55 text
  • To prevent locked accelerators in cal. .50 aircraft guns, a new-design accelerator stop B7161301 and stop lock B7161300 are now used in place of the sear stop pin assembly. When these parts are used, the modified breech lock (with a slot) B7161302 must be used.
  • Page 56 text
  • Some firing pins B7310080 were manufactured with four flats on the sides to provide space in the bolt tunnel for dirt to collect and thus prevent jamming of the pin.
  • Driving Spring Rod With Springs Assembly - Exploded View - Figure 43 - Page 57 - RA PD 91904
  • ROD, DRIVING SPRING - B147508
  • PIN, RETAINING, DRIVING SPRING ROD - A152899
  • SPRING, DRIVING, OUTER - B147509
  • SPRING, DRIVING, INNER - B147510
  • HEAD, DRIVING SPRING ROD - A152901
  • COLLAR, DRIVING SPRING ROD - A152900
  • PIN, STOP, DRIVING SPRING ROD COLLAR - A152898
  • Bolt Handle - Showing Dimensions- B8583 - Figure 44 - Page 59 - RA PD 50598
  • title p/n only
  • Accelerator Stop Assembly and Bolt - Exploded View - Figure 45 - Page 60 - RA PD 91906
  • LOCK, ACCELERATOR STOP - B7161300
  • STOP, ACCELERATOR - B7161301
  • OIL BUFFER GROUP
  • Bolt Group - Exploded View - Figure 46 - Page 61 - RA PD 91828
  • A - EXTRACTOR, ASS'Y - B8959
  • B - SWITCH, BOLT - C4062
  • C - STUD, BOLT SWITCH - A13529
  • D - STOP, SEAR, ASS'Y - B8788
  • E - LEVER, COCKING - B9718
  • F - SEAR - C4067
  • G - SPRING, SEAR - A9524
  • H - PIN, STOP, EXTRACTOR - A9385
  • I - BOLT, ALTERNATE FEED - D28256
  • J - PIN, COCKING LEVER - B147762
  • K - SLIDE, SEAR - A351220
  • L - PIN, FIRING - B7310080
  • M - EXTENSION, FIRING PIN, ASS'Y - B8976
  • N - PLATE, RECOIL - A152858
  • OIL BUFFER GROUP - Section VIII
  • Page 63 text
  • Oil Buffer Tube Lock Assembly - C145325
  • Oil Buffer Body Group - Exploded View - Figure 49 - Page 64 - RA PD 90812
  • BODY, OIL BUFFER - C8063
  • GUIDE, OIL BUFFER - B9715
  • LOCK, SPRING, OIL BUFFER BODY - A9266
  • LOCK, OIL BUFFER TUBE ASSEMBLY - C145325
  • DEPRESSOR, BREECH LOCK - B9712
  • RIVET, BREECH LOCK DEPRESSOR - A9283
  • PIN, ACCELERATOR - A9276
  • SPRING, ACCELERATOR PIN - A9357
  • ACCELERATOR - C8141
  • Oil Buffer Assembly With Spring and Guide - Figure 51 - Page 65 - RA PD 91829
  • BUFFER, OIL, ASSEMBLY - C4077
  • SPRING, OIL BUFFER - B9832
  • GUIDE, OIL BUFFER SPRING - A9518
  • KEY, OIL BUFFER SPRING GUIDE - A9520
  • Page 69 text
  • If a heavy-barrel gun delivers the normal rate of fire (450 to 550 rounds per minute), the gun may be considered in good operating condition. If sluggish operation or stoppages are encountered, disassemble the gun and inspect all moving parts for rough surfaces, burs, or insufficient lubrication. If any of these conditions are found, they must be corrected. If the gun still operates sluggishly or if stoppages occur, the oil and the following parts (fig. 56) should be removed from the oil buffer:
    A9279A ..... PACKING, oil buffer gland
    A9297 ........ RING, oil buffer packing gland
    A9360 ........ SCREW, oil buffer relief valve
    A9299 ........ SPRING, oil buffer packing gland
    A9393 ........ SPRING, oil buffer relief valve
    A9528 ......... VALVE, relief, oil buffer
  • NOTE A: Packing A153162 and washer A153161 may be found assembled in place of packing A9279A and ring A9297. These parts should be removed.
  • NOTE B: Previous instructions have directed removal of the oil buffer tube filler screws A9361. These screws are needed to prevent dirt and other extraneous matter from entering the oil buffer tube. Therefore, all oil buffers from which the screws have been removed should be cleaned and the screws replaced.
  • Components removed should be turned in to the local Post Ordnance Officer, who will forward them to Raritan Arsenal.
  • Fitting New Oil Buffer Tube Lock Assembly.
    A new oil buffer tube lock assembly C145325 (fig. 57) has been provided to replace oil buffer tube lock assembly B8787 or B8787A. The old oil buffer tube lock causes stoppage by slipping rearward during the firing of tbe cal. .50 Browning machine gun, and us not fully depressing the accelerator. This condition results in accelerator tips jamming in the breech lock slot in the bolt. The new oil buffer tube lock assembly consists of two components riveted together, namely, oil buffer tube lock latch B284610, and oil buffer tube lock body B284606. The function of the latch is to prevent the oil buffer tube lock assembly from sliding rearward while the gun is functioning.
  • Page 72 text
  • Present manufacture of heavy-barrel guns is omitting the oil buffer gland packing, packing gland ring, packing gland spring, relief valve, relief valve spring, relief valve screw, and oil in addition to the oil buffer piston valve assembly.
  • (water-cooled) Cylindrical-type packing A153162 is assembled in the same order, but with a washer A153161 and a spring A153163 in place of the gland ring and spring used with the old conical-type packing.
  • Oil Buffer Assembly - Exploded View - Figure 56 - Page 73 - RA PD 91830
  • A - SCREW, FILLER, OIL BUFFER TUBE, ASSEMBLY - B147888
  • B - TUBE, OIL BUFFER - C8146
  • C - PIN, OIL BUFFER PISTON HEAD NUT - A9380
  • D - NUT, OIL BUFFER PISTON HEAD - A9267
  • E - VALVE, OIL BUFFER PISTON, ASSEMBLY - B8969
  • F - KEY - A9784 {PART OF VALVE ASSEMBLY)
  • G - HEAD, OIL BUFFER PISTON ROD - B17169
  • H - CAP, OIL BUFFER TUBE - B147845
  • I - SPRING, OIL BUFFER PACKING GLAND - A153163
  • J - VALVE, RELIEF, OIL BUFFER - A9528
  • K - SPRING, OIL BUFFER RELIEF VALVE - A9393
  • L - SCREW, OIL BUFFER RELIEF VALVE - A9360
  • M - WASHER, OIL BUFFER PACKING GLAND - A153161
  • N - PACKING, OIL BUFFER GLAND - A153162
  • O - PLUG, OIL BUFFER PACKING GLAND - A9277
  • P - ROD, OIL BUFFER PISTON - B9830
  • Q - PIN, OIL BUFFER PISTON ROD - A9379
  • Oil Buffer Tube Lock Assembly C145325 - Figure 57 - Page 75 - RA PD 88157
  • BODY, LOCK - B284606
  • RIVET - A312673
  • LATCH - B284610
  • BARREL AND BARREL EXTENSION GROUP - Section IX
  • Page 76 text
  • The old-type breach lock B8925 had two bevels on the top front edge; lock of later modification has but one bevel. New-type lock B7161302, used in aircraft guns, has one bevel and a slot in the bottom for clearance of the accelerator stop assembly when used in place of the sear stop assembly. New-type lock must be used when accelerator stop assembly is used. Figure 60 shows old type and new type with slot. Modified old type is same as new type but without the slot.
  • Types at Barrels - Figure 58 - Page 77 - RA PD 91820
  • BARREL ASSEMBLY D28272 FOR CAL .50 AIRCRAFT GUN M2
  • BARREL D35348A FOR CAL .50 AIRCRAFT GUN M2
  • BARREL ASSEMBLY D28271 FOR WATER-COOLED GUN M2
  • BARREL D28253A FOR HEAVY BARREL GUN M2
  • Barrel Extension Group - Exploded View - Figure 59 - RA PD 91831 - Page 77
  • SHANK, BARREL EXTENSION - B9728
  • EXTENSION, BARREL - D28254
  • SPRING, BREECH LOCK PIN - A9357
  • SPRING, LOCKING BARREL - B8908
  • LOCK, BREECH - B8925
  • Old-type Breech Lock, And New Type Used With Aircraft Guns - Figure 60 - Page 78 - RA PD 88168
  • LOCK, BREECH (OLD TYPE) - B8925
  • LOCK, BREECH (NEW TYPE) - B7161302
  • Page 80 text
  • Disposition Of Unserviceable Barrels: Unserviceable barrel assemblies which have a sleeve assembled to the muzzle end may be disposed of locally after the sleeves are removed. These sleeves should be forwarded to Springfield Armory for reassembly to new barrels.
  • Page 81 text
  • Cal .50 Chamber Reamer (locates old bullet seat 1/4" forward to meet 2nd March 1942 drawing C64348) - C121020
  • COVER GROUP - Section X
  • Cover Group - Exploded View - Figure 65 - Page 87 - RA PD 91832
  • A - KEY, COVER LATCH SHAFT - A13544
  • B - LEVER, COVER LATCH SHAFT - A13586
  • C - PIN, COVER LATCH SHAFT LEVER - A13587
  • D - SHAFT, COVER LATCH - A13587 {same p/n as above}
  • E - LEVER, FEED, BELT - C64278
  • F - PIN, COTTER (3/32" X 3/4") - 103373
  • G - SPRING, COVER LATCH - B8931
  • H - SPRING, COVER EXTRACTOR - B9741
  • I - SPRING, BELT FEED LEVER PLUNGER - A13516
  • J - PLUNGER, BELT FEED LEVER - A13515
  • K - SPRING, BELT FEED PAWL PIN - A9357
  • L - PIN, BELT FEED PAWL - A13519
  • M - ARM, BELT FEED PAWL - B8914
  • N - PIN, BELT FEED PAWL ARM - A13517
  • O - PIN, LOCATING, BELT FEED PAWL ARM - A13518
  • P - PAWL, FEED, BELT - B8913
  • Q - SPRING, BELT FEED PAWL - A9351
  • R - STUD, BELT FEED PAWL 5PRING - A9363
  • S - SLIDE, FEED, BELT - B147756
  • T - PIN, COTTER (1/8" X 7/8") - 108630
  • U - RIVET, COVER BRACKET - A152980
  • V - BRACKET - A152752
  • W - LATCH, COVER - B8928
  • X - PIN, COTTER (1/16" X 7/16") - 137130
  • Y - WASHER, COVER LATCH SHAFT - A13545
  • Z - COVER - D28258
  • AA - STUD, COVER LATCH SPRING - A9366
  • BB - CAM, EXTRACTOR, COVER - C64279
  • CC - STUD, PIVOT, BELT FEED LEVER - A9395
  • DD - PIN, BELT FEED LEVER PIVOT STUD - A9384
  • EE - WASHER, BELT FEED LEVER PIVOT STUD - A9398
  • FF - RIVET, COVER EXTRACTOR CAM - A9282
  • GG - STUD, COVER EXTRACTOR SPRING - A9365
  • HH - PIN, COVER - A9371
  • Special Cover Latch - Figure 67 - Page 88 - RA PD 88163
  • LATCH, COVER - B7161236
  • Short Round Device T1E4 Installed In Cover - Figure 69 - Page 89 - RA PD 88154
  • DEVICE, SHORT ROUND - T1E4
  • Short Round Device T13 Assembled To Cover - Figure 71 - Page 90 - RA PD 88156
  • DEVICE, SHORT ROUND - T13
  • BRACKET, COVER - A152752
  • Page 94 text
  • NOTE; Belt feed slide B261110 is available for all guns to improve feeding operations and insure continuous feeding when a long ammunition belt is used. It also increases the load-lifting capacity of the gun. It is identified by a 1/8-inch hole drilled through the face of the slide, and by the fact that the belt feed lever slots on the two sides of the slide are no longer in line. Detailed information can be found in TM 9-225.
  • CASING GROUP - Section XI
  • Page 94 text
  • NOTE: The casing group includes the receiver group, together with the barrel jacket, water jacket, barrel support, or other groups which are attached to it to comprise the type of gun in question.
  • Page 95 text
  • NOTE: In some aircraft guns of present manufacture the split belt holding pawl is used. Belt holding pawl pin B7160030 has a split front end and a bend in the rear to act as a withdrawing handle.
  • Split Belt Holding Pawl and Present-type Belt Holding Pawl Pin - Exploded View - Figure 75 - Page 96 - RA PD 91908
  • PAWL, BELT HOLDING, L.H. - B7160625
  • PAWL, BELT HOLDING, R.H. - B7160625
  • SLEEVE, BELT HOLDING PAWL - B7160627
  • SPRING, BELT HOLDING PAWL - B7160628
  • PIN, BELT HOLDING PAWL - B7160030
  • Right-hand Rear Cartridge Stop Assembly - Exploded View - Figure 76 - Page 97 - RA PD 91834
  • STOP, CARTRIDGE, REAR, R.H - C77408
  • PAWL, ALIGNING, CARTRIDGE - B8975
  • PIN, CARTRIDGE ALIGNING PAWL - A13612
  • SPRING, CARTRIDGE ALIGNING PAWL - A13613
  • PLUNGER, CARTRIDGE ALIGNING PAWL - A13611
  • Removing Trigger Bar Pin Assembly (Old Type) - Figure 78 - Page 98 - RA PD 91836
  • PIN, TRIGGER BAR ASS'Y - B8683
  • New-type Trigger Bar Pin Assembly B7310075 - Figure 79 - Page 98 - RA PD 83148
  • BODY - A7310072
  • LOCK - A7310074
  • BALL - A7312241
  • SPRING - A7310073
  • Bolt Latch Group - Exploded View - Figure 80 - Page 100 - RA PD 91837
  • A - SCREW, STOP - A13622
  • B - NUT, STOP SCREW - A13623
  • C - LATCH, BOLT - C4060
  • D - PLUNGER - A13524
  • E - SPRING, PLUNGER - A13525
  • F - PIN - A13523
  • G - ROD - B8919
  • H - SPRING - A13527
  • I - PIN, COTTER (3/32" X 3/4") - 103373
  • J - BRACKET - C4061
  • K - NUT, ROD - A13526
  • Barrel Jacket With Front Bearing Assembly - Exploded View - Figure 81 - Page 100 - RA PD 91838
  • BEARING, BARREL, FRONT - A8910
  • SCREW, FRONT BARREL BEARING - A13655
  • BEARING, BREECH - B8921
  • JACKET, BARREL - D28255
  • Aircraft Machine Gun Booster, Cal. .50 - Exploded View - Figure 82 - Page 101 - RA PD 49039
  • SCREW, FRONT BARREL BEARING (2) - A153192
  • SLEEVE, BOOSTER - C7160102
  • GUIDE, BARREL SLEEVE - A196242
  • WASHER, LOCK, BOOSTER - A196243
  • HOUSING, BOOSTER PLUG - C7160044
  • PLUG, BOOSTER - B243590
  • Page 102 text
  • Booster Assembly - A038-7160043
  • Front Barrel Bearing Group (Water-cooled Guns) - Exploded View - Figure 84 - Page 103 - RA PD 91840
  • JACKET, WATER, ASSEMBLY - D28274
  • BEARING, BARREL, FRONT - B8900
  • PACKING, BARREL, FRONT - A135710
  • RING, MUZZLE PACKING - A13548
  • GLAND, MUZZLE - B8938
  • LOCK, FRONT BARREL BEARING - B8901
  • LOCK, MUZZLE GLAND - A13547
  • SCREW, FRONT BARREL BEARING LOCK - A13501
  • NUT, JAM, FRONT BARREL BEARING LOCK SCREW - A13502
  • Figure 85 - Page 103 - RA PD 91841
    Water Jacket Group and Steam Tube Group - Phantom and Exploded Views
  • SCREW, LOCK, STEAM TUBE SUPPORT - A9358
  • PLUG, STEAM TUBE BRACKET - A13553
  • BRACKET, STEAM TUBE - B8941
  • SUPPORT, STEAM TUBE, FRONT - C4069
  • SUPPORT, STEAM TUBE, REAR - B8942
  • TUBE, STEAM - C4068
  • Water Jacket Removed From Receiver (W-C) - Figure 86 - Page 104 - RA PD 91842
  • JACKET, WATER, ASSY - D28274
  • SHIM, TRUNNION BLOCK- B8982
  • RECEIVER, ASS'Y - D35480
  • Barrel Support Group Removed From Receiver - Exploded View (HB) - Figure 87 - Page 104 - RA PD 91843
  • SCREW, LOCK, BREECH BEARING - A13530
  • SHIM, TRUNNION BLOCK - B8982
  • SUPPORT, BARREL - C4091A
  • BARREL - D28253
  • BEARING, BREECH - B8920
  • RECEIVER, ASSEMBLY - D35480
  • Retracting Slide Group - (Right-hand Assembly) - Showing Alternate New-type Handle Assembly - Exploded View - Figure 88 - Page 105 - RA PD 91844
  • A - SLIDE RETRACTING - B8991
  • 8 - STUD, RETRACTING SLIDE LEVER - B8992
  • C - STOP, RETRACTING SLIDE LEVER - A13694
  • D - BRACKET, RETRACTING SLIDE - C46029
  • E - BOLT, RETRACTING SLIDE BRACKET - A13681
  • F - PIN, COTTER (1/16" x 3/4") - 103362
  • G - NUT, RETRACTING SLIDE - A13686
  • H - SPRING, RETRACTING SLIDE PLUNGER - A13693
  • I - PLUNGER, RETRACTING SLIDE - B8990
  • J - PIN, RETRACTING SLIDE PLUNGER - A13687
  • K - STUD, RETRACTING SLIDE - B8993
  • L - SCREW, RETRACTING SLIDE BRACKET, FRONT - A13419D
  • M - LEVER, RETRACTING SLIDE - B147085
  • N - WASHER, RETRACTING SLIDE GRIP - A13696
  • O - SCREW, RETRACTING SLIDE BRACKET, REAR - A13419E
  • P - SPRING, RETRACTING SLIDE LEVER, R.H. - A13692
  • Q - PIN, TAPER (NO. 4 X 3/4") - 103603
  • R - WIRE, LOCKING (24 IN.) - A7310038
  • S - WASHER, RETRACTING SLIDE LEVER STUD - A13697
  • T - FERRULE, RETRACTING SLIDE GRIP - A9517
  • U - GRIP, RETRACTING SLIDE - A13684
  • V - TUBE, RETRACTING SLIDE GRIP - A13695
  • W - BOLT, RETRACTING SLIDE GRIP, ASS'Y - B147597
  • X - HANDLE, RETRACTING SLIDE, ASS'Y (NEW TYPE) - B313800
  • Operating Slide Group Assembly - Parts Arranged for Assembly to Left Side Plate - Exploded View - Figure 89 - Page 107 - RA PD 91845
  • A - ROLLER - A13425
  • B - PIN, ROLLER - A13415
  • C - PIN, COTTER (1/16" X 7/16") - 137130
  • D - SPRING, PLUNGER - A13423
  • E - PLUNGER, HANDLE - A13417
  • F - STOP - A13420
  • G - GUIDE - B8745
  • H - SCREW, GUIDE, REAR, UPPER - A13419B
  • I - SCREW, GUIDE, REAR, LOWER - A13419C
  • J - BAR - C3946
  • K - HOOK - A13422
  • L - GUIDE, FRONT - A13421
  • M - SCREW, GUIDE, FRONT - A13419A
  • N - WIRE, S. - BFWXIA
  • O - PIN, STOP, HANDLE - A13418
  • p - PIN, HINGE, HANDLE - A13416
  • Q - HANDLE - C3945
  • R - RIVET, S, CK-HD. , 1/8" X 3/8", (missing)
  • S - SPRING - A9804
  • T - PIECE, BACK, GUIDE - A13609
  • Barrel Carrier Assembly - Exploded View - Figure 90 - Page 107 - RA PD 91846
  • A - HANDLE, REAR - B8903
  • 8 - SLEEVE, HANDLE, ASS'Y - C4083
  • C - HANDLE, FRONT - B8567
  • D - BOLT - A13503
  • E - SPRING, BOLT - B8902
  • F - PIN, RETAINING, BOLT - A13507
  • G - SLEEVE, ASS'Y - C4093
  • H - PIN, BOLT HEAO - A13505
  • I - HEAD, BOLT - A13504
  • Side Plate Trigger Assembly - Exploded View - Figure 91 - Page 108 - RA PD 91847
  • A - BOLT - A130091
  • B - HOUSING - C4074
  • C - PIN - A130094
  • D - SPRING - A13616
  • E - CAM - B128712
  • F - SPRING, SLIDE - A13617
  • G - PIN, SLIDE SPRING (IN EXTENSION) - A13580
  • H - PIN, SLIDE SPRING (IN CAM) - A13580
  • I - EXTENSION - B8947
  • J - SCREW, EXTENSION - A130097
  • K - HANDLE - B8899
  • L - NUT - A130092
  • M - PIN, COTTER (1/16" X 1") - 103363
  • N - SLIDE - B128715
  • Page 109 text
  • Side Plate Trigger Assembly - A037-02-01930 (included with antiaircraft mounts)
  • Rear Sight Group For Heavy - Barrel Guns - Exploded View - Figure 92 - Page 110 - 111 - RA PD 91848
  • A - PIN, RETAINING, TELESCOPIC SIGHT CLAMP SCREW - A152409
  • B - SCREW, CLAMP, TELESCOPIC SIGHT - A152410
  • C - SPRING, TELESCOPIC SIGHT CLAMP SCREW - A15241
  • D - HANDLE, TELESCOPIC SIGHT CLAMP SCREW - A1 52408
  • E - PIN, REAR SIGHT WINDAGE KNOB - A13700
  • F - KNOB, REAR SIGHT WINDAGE SCREW - B8809
  • G - SPRING, REAR SIGHT WINDAGE CLICK PLUNGER - A13154
  • H - PLUNGER, REAR SIGHT WINDAGE CLICK - A13155
  • I - SCALE, WINDAGE, REAR SIGHT - A13607
  • J - SCREW, REAR SIGHT WINDAGE 5CALE - A13167
  • K - SPRING, REAR SIGHT BASE - A13619
  • L - LEAF, REAR SIGHT - D28281
  • M - PIN, RETAINER, REAR SIGHT ELEVATING SCREW - A13162
  • N - CLICK, REAR SIGHT ELEVATING KNOB - A13161
  • O - SCREW, ELEVATING, REAR SIGHT - B8973
  • P - PIN, REAR SIGHT ELEVATING KNOB - A13166
  • Q - KNOB, REAR SIGHT ELEVATING SCREW - A13610
  • R - SLIDE, REAR SIGHT - C4096
  • S - NUT, HALF, REAR SIGHT - B8974
  • T - SCREW, REAR SIGHT BASE - A153191
  • U - SCREW, REAR SIGHT COVER PLATE - A152658
  • V - PLATE, COVER, REAR SIGHT - A152412
  • W - STOP, REAR SIGHT LEAF - A13253
  • X - SCREW, WINDAGE, REAR SIGHT - A13160
  • Y - CLAMP, TELESCOPIC SIGHT - B8584
  • Z - SPRING, TELESCOPIC SIGHT CLAMP - A13620
  • AA - BASE, REAR SIGHT, ASSEMBLY - D28338
  • Page 113 text
  • Old-type single spring A9522 used with pawl B8916.
  • New-type, cadmium-plated, twin springs A153146 used with pawl B261098 (do not confuse these twin springs with springs B7160628 used with new-type split pawl).
  • Page 125 text
  • PACKING RING ADJUSTING WRENCH - 41-W-3242-500
  • BOOSTER ASS'Y (AIRCRAFT GUNS) - A038-7160043
  • Page 126 text
  • BARREL HOLDING WRENCH - 41-W-530
  • Receiver Group
  • Page 128 text
  • FLASH HIDER - 1-H-1765
  • Receiver Group - Exploded View - Figure 100 - Page 128-129 - RA PD 91839
  • A - SCREW, TOP PLATE COVER (3) - A13608
  • B - COVER, TOP PLATE - B8939
  • C - PLATE, TOP - D28263
  • D - RIVET, BOLT LATCH BRACKET, SHORT (5) - A13522
  • E - BRACKET, BOLT LATCH - C4061
  • F - RIVET, TOP PLATE (16) - A9500
  • G - STOP, TRIGGER BAR, REAR - A9390
  • H - STUD, TOP PLATE BRACKET - A9367
  • I - BAR, TRIGGER - B257592
  • J - STOP, TRIGGER BAR, FRONT - A9391
  • K - BRACKET, TOP PLATE - C4070
  • L - RIVET, TOP PLATE BRACKET (2) - A9292
  • M - PIN, TRIGGER BAR, ASSEMBLY - B8683
  • N - STOP, BOLT - A9392
  • O - SPRING, SWITCH - B8943
  • P - PLATE, SIDE, L.H. - D28262
  • Q - SWITCH - B147461
  • R - NUT, SWITCH PIVOT - A13556
  • S - PIN, COTTER (1/16" X 3/4") - 103362
  • T - CAM, EXTRACTOR - A9373
  • U - RIVET, EXTRACTOR CAM (2) - A9501
  • V - BRACKET, BELT HOLDING PAWL, L.H. - C4095
  • W - PAWL, COVER DETENT, ASSEMBLY - B8515
  • X - SPRING, BELT HOLDING PAWL - A153146
  • Y - SPRING, COVER DETENT PAWL - A13520
  • Z - PAWL, HOLDING, BELT - B261098
  • AA - COVER, TRUNNION BLOCK - A13588
  • BB - PIN, TRUNNION BLOCK COVER - A13546
  • CC - RIVET, TRUNNION BLOCK, LENGTH 2.52" (4) - A13558
  • DD - PIN, COTTER (1/16" X 3/4") - 103362
  • EE - SCREW, LOCK, BREECH BEARING - A152829
  • FF - SPRING, TRUNNION BLOCK LOCK - A13566
  • GG - LOCK, TRUNNION BLOCK - A13565
  • HH - SHIM, TRUNNION BLOCK - B8951 (A TO M)
  • JJ - ADAPTER, TRUNNION - C4052
  • KK - RIVET, BOTTOM PLATE (16) - A9387
  • LL - PLATE, BOTTOM - D28257
  • MM - RIVET, BOLT LATCH BRACKET, LONG (4) - A13521
  • NN - PLATE, SIDE, R.H. - D28261
  • OO - BOLT, BREECH LOCK CAM - A152938
  • PP - CAM, LOCK, BREECH, A5SEMBLY - B147583
  • QQ - PIN, COTTER (1/8" X 1-1/2") - 103387
  • RR - NUT, BREECH LOCK CAM BOLT - A152939
  • SS - RIVET, BELT HOLDING PAWL BRACKET, SHORT (2) - A13698
  • TT - STOP, CARTRIDGE, REAR, R.H., ASSEMBLY - C77409
  • UU - PIN, BELT HOLDING PAWL, ASSEMBLY - B8963
  • VV - BRACKET, BELT HOLDING PAWL, R.H. - B128730
  • WW - STOP, CARTRIDGE, FRONT - A13539
  • XX - RIVET, TRUNNION BLOCK, LENGTH 0.605" (18) - A9799
  • YY - PLUG, BUNTER - A13572
  • ZZ - RIVET, BELT HOLDING PAWL BRACKET, LONG (6) - A13598
  • AB - PIN, COTTER (3/32" X 3/4") - 103373
  • AC - BLOCK, TRUNNION - D28264
  • AD - STRIPPER, LINK - A13541
  • AE - STOP, CARTRIDGE, REAR - A13540

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