M2 Milspec Mil G 1298a

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MIL-G-1298A10 OCTOBER 1955

SUPERSEDINGMIL-G-129822 JULY 1949

MILITARY SPECIFICATION

GUNS, MACHINE, (CALIBRE .50, BROWNING, M2,

HEAVY BARREL

This specification has been approved by the Department of Dcfense and is man-datory for use by the Departments of the Army, the Navy, and the Air Force.

1. SCOPE

1.1 Scope. This specification covers auto-matic, recoil-operated, link-belt fed, air-

cooled caliber .50 heavy barrel machinegunsfor fixed or flexible installation on groundmounts and combat vehicles.

1.2 Classification. Machineguns shall be ofthe following types, as specified (see 6.1):

Gun, Machine, Cal .50, Browning, M2,Heavy Barrel, Flexible

Gun, Machine, Cal .50, Browning, M2,

Heavy Barrel, Fixed

Gun, Machine, Cal .50, Browning, M2,Heavy Barrel, Turret Type

2. APPLICABLE DOCUMENTS

2.1 The following documents, of the issuein effect on date of invitations for bids, form

a part of this specification:

SPECIFICATIONS

MILITARY

MIL-W-13855

STANDARDS

MILITARY

Weapons, Small Arms,

General Specificationfor.

MIL-STD-105 Sampling Procedures

and Tables for In-spection by At t r i -

butes.

DRAWINGS

ORDNANCE CORPS

51-70-1A Gun, Machine, Cal .50,Browning, M2, HeavyBarrel, Flexible

51-71-1A Gun, Machine, Cal .50,Browning, M2, HeavyBarrel, Fixed

51-119-1A Gun, Machine, Cal .50,Browning, M2, HeavyBarrel, Turret Type

C-5520627 Compress ion Cyl inderHolding Fixture

A-5153086 Spring, Belt Feed Test

(Copies of specifications, standards, drawings, andpublications required by contractors in connectionwith specific procurement functions should be ob-tained from the procuring activity or as directed bythe contracting officer.)

3. REQUIREMENTS

3.1 Design and manufacture.

3.1.1 General. Components and assemblies

shall conform to the materials, dimensions,

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MIL-G-1298A

tolerance limits, physical properties, degreeof surface roughness, and final protectivefinishes specified on the drawings andshall be in accordance with SpecificationMIL-W-13855.

3.1.2 Marking. Unless otherwise specified,

each machinegun, and each component there-of for which markings are prescribed, shallbe clearly marked in accordance with thedrawings and Specification MIL-W-13855.

(See 6.1.)

3.1.3 Barrel assembly. The barrel boreshall be straight, and the lands shall be welldefined. The bore shall be free of scratches,cracks, seams, and pits. Pockets, rings, andbulges not exceeding .0005 inch in depth or

two inches in length shall be allowed in thebore, provided they do not occur within fourinches of the muzzle end. Slight scratches or

marks, occurrng in a chamber which other-wise meets the surface roughness require-ments, shall be permitted provided they donot cause marks on the case of a high pres-sure test cartridge fired in the chamber.

3.1.4 Cocking lever retraction. The cockinglever shall retract the firing pin assembly,when operated by hand, sufficiently to insureengagement of the firing pin extension hookto the sear hook.

3.1.5 Firing pin. The point of the firing pinshall be smooth and well rounded. There shallbe no hand stoning of the firing pin point.

3.1.6 Firing pin protrusion. The firing pinprotrusion shall be such as to insure propercartridge ignition.

3.2 Springs. When specified on the draw-ings, springs shall be subjected to an en-durance test.

3.3 Carburization. Carburized componentsshall have the depth of case and the hard-ness prescribed on the drawings.

3.4 Firing pin release. The firing pin as-

sembly shall be released by a load not ex-

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ceeding 35 pounds applied to the sear slideand by a load not exceeding 23 pounds appliedto the sear.

3.5 Striker indent. The indent, taken in

copper compression cylinders of 99.90 percentpure copper, soft annealed, shall be withinthe range of 0.017 to 0.023 inch.

3.6 Interchangeability. All components andassemblies on lists supplied by the procuringagency, which substantially contain thoseparts maintained for replacements, shall beinterchangeable. (See 6.1.)

3.7 Headspace. The distance between therear face of the barrel and the face of thebolt shall be within the limits specified in

4.3.7.

3.8 Timing. Machineguns shall meet thetiming requirements specified in 4.3.8.

3.9 High pressure resistance. Guns andcritical spare parts shall be capable of with-standing the disruptive pressures of a proofcartridge. After proof firing, components andassemblies shall be checked for cracked andweakened conditions and the recoil plate inthe face of the bolt shall be checked forsetback.

3.10 Functioning. Machineguns shall func-tion smoothly and properly without mal-functions or breakages, and shall have sufi-cient power to withstand the belt pull testspecified in 4.3.10.

3.11 Cyclic rate of fire. Machineguns shallmaintain an average rate of fire of 450 to600 shots per minute.

3.12 Targeting. Machineguns shall meetthe targeting requirements specified in 4.3.12.

3.13 Accuracy. Machineguns shall meet theaccuracy requirements specified in 4.3.13.

3.14 Endurance. Machineguns shall be cap-able of passing an endurance test of 10,000



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rounds without substitution of any com-ponents, and without malfunctions, in excessof the limits shown in table 1. The machine-gun shall complete the first 5,000 rounds ofthe test without replacement of any com-ponents.

3.15 Barrel erosion. Barrels shall be cap-able of firing the specified number of roundswithout excessive deterioration, and shallmeet the specified accuracy and velocity re-quirements. (See 6.1.)

3.16 Workmanship. Finished machinegunsshall be free of defects which may affect ser-viceability, functioning, operation, safety, orappearance.

TABLE I.Malfunctions, nonacceptable conditions, , andunserviceable components (see note)

TABLE I.Malfunctions, nonacceptable conditions, andunserviceable components (see note) - Continued

Note. When malfunctions (within the allowances of

table I are are traceable to particular components, it ispermissible to replace such component and recordthem as unserviceable, subject to limitations of table

I. When it is definitely established by the inspectorthat previously recorded malfunctions are attri-butable to an unserviceable component, such mal-

functions shall not be counted against the machine-gun being tested, provided that they occurred notmore than 200 rounds prior to replacement of the

unserviceable component. However, such malf unc-tions shall remain recorded and properly identified.

4. QUALITY ASSURANCE PROVISIONS

4.1 Sampling.



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4.1.1 Lot. Unless otherwise specified, a lotshall consist of not more than 101 machine-

guns for the initial lot and not more than501 machineguns for each subsequent lot.

4.1.2 Inspection sample. Where practicable,inspection sample sizes shall be in accord-

ance with Standard MIL-STD-105. However,the inspector may subject all or part of anylot of components or assemblies to such in-spection as he deems necessary to determinecompliance with this specification.

4.1.3 Test samples. Unless otherwise spe-cified, the number of test samples shall beas specified for each test.

4.2 Inspection. Machineguns shall be visu-ally inspected for completeness of manufac-ture, assembly, finish, and workmanship.The chamber and bore shall be examined forrust, pits, powder fouling, burrs, and otherdefects. Each machinegun shall be operatedby hand to ascertain that the final adjust-

ments have been made to assure properoperation. Components shall be inspected asnecessary to assure compliance with drawingrequirements. Before final acceptance of anylot, the inspector shall make whatever finalvisual inspection deemed necessary to assure

that the machineguns have undergone allinspection and tests prescribed therefor, andthat the machineguns have been thoroughlycleaned and prepared for shipment as re-quired by section 5.

4.3 Tests.

4.3.1 General.

4.3.1.1 Ammunition. Ammunition used inall firing tests, except the proof firing test,shall be caliber .50 Government, standard

service ammunition specified by procurementdocuments. (See 6.1.) Proof firing ammuni-tion shall be as specified in 4.3.9.

4.3.1.2 Mounts. Unless otherwise specified,all firing tests except the targeting and ac-curacy tests shall be accomplished from

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Machine Gun Tripod Mount, Cal. 50, M3.The mount shall & suitably braced duringfiring.

4.3.1.3 Concurrent tests.

4.3.1.3.1 Functioning and cyclic rate of firetest. The functioning test and the cyclic rateof fire test may be fired concurrently.

4.3.1.3.2 Targeting and accuracy ted. Thetargeting test and the accuracy test may befired concurrently at a range of 100 feet.

4.3.2 Spring test. Springs designated bythe drawings shall be tested as specified on

the applicable drawings. The contractor shallprovide suitable equipment for making thesetests, and shall record the conditions andresults of each test.

4.3.3 Carburization test. A representative

sample consisting of not less than 3 itemsof each lot of each carburized and hardenedcomponent shall be fractured and the depthof case determined by microscopic examina-tion. Test samples may be components re-

jected for other reasons.

4.3.4 Firing pin release test. Ten bolt as-semblies, taken at random by the inspectorfrom each lot of machineguns, shall be sub-

jected to the firing pin release test. Using anapproved fixture with a suitable indicatingdial, a load shall be applied slowly and uni-formly at the following points until the firingpin is released: first, to the sear slide onone side; then, with the sear slide reversed,to the sear slide on the other side; and next,directly to the sear from the top. The loadshall be applied 5 times at each of the threepoints.

4.3.5 Striker indent test. The striker in-dent shall be taken on at least 10 machine-guns of each lot. The indent, taken in copper

compression cylinders inserted in a holdingfixture conforming to Drawing C5520627, is

computed by measuring the distance from

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the original surface (before indentation) ofthe cylinder to the bottom of the impression.

4.3.6 Interchangeability test .

4.3.6.1 Machineguns. Ten machinegunstaken at random by the inspector from eachlot shall be tested for interchangeability ofcomponents and assemblies. Tests may bemade less frequently when consistent satis-factory results have been proven and whenauthorized by the procuring agency.

4.3.6.2 Procedure. Components and assemb-

lies shown in the list to be furnished by theprocuring agency shall be disassembled fromthe weapons. Components of each kind shallbe placed together and mixed. The machine-

guns shall be reassembled without selecting,fitting, or altering any component in any wayexcept that hand fitting will be allowed onnot more than 20 percent of the machine-guns, provided that, as a result, no compo-nent or assembly is rendered unsuitable forassembly in other machineguns. The as-sembled machineguns shall operate and func-tion properly.

4.3.6.3 Spare parts. At least 20 percent ofthe machineguns previously tested for inter-changeability, disassembled as necessary,shall be reassembled using components desig-nated for use as spare parts. There shall beno hand fitting, and the machineguns shalloperate and function properly.

4.3.6.4 Guns and spare parts concurrentlymade by two or more manufacturers shallbe subjected to an interplant interchange-ability test. Samples required by procure-ment documents (see 6.1), representing gunsand parts from concurrent manufacturers,shall be placed together, mixed, and testedas prescribed in 4.3.6.2 and 4.8.6.3.

4.3.6.5 All weapons assembled from inter-changed parts shall be subjected to the func-tion and accuracy firing tests, and whenapplicable, to the targeting firing test. Thecontractor shall be responsible for the con-

ditioning of weapons and parts subjected tothe interchangeability teat.

4.3.7 Headspace test. With the bolt re-tracted until the barrel extension and trun-

nion block are separated approximately 1/16inch, each machinegun shall have the dis-tance between the rear face of the barreland the face of the bolt set within the limitsof the headspace gage (0.202 inch Go and0.206 inch No Go.)

4.3.8 Timing test. The timing test shall beperformed on each machinegun after settingthe headspace. Releasing of the firing pinassembly shall be accomplished through themedium of the trigger bar. Machineguns not

equipped with trigger bars shall be tested

for timing by using a side plate solenoid setfor a protrusion of 0.290 to 0.320. In addition, not less than 10 percent of each lot ofheavy barrel fixed and turret type machine-guns shall be checked for proper timing bymeans of a side plate trigger set for a mini-mum protrusion of 0.285 inch. Protrusionshall be measured from the mounting faceto the top of the plunger.

4.3.8.1 With the 0.116 inch No Fire gageinserted between the front face of the barrelextension and the trunnion block, an attemptshall be made to release the firing pin as-sembly. The firing pin assembly shall notrelease on the first impulse of the firing me-chanism. Remove the No Fire gage, re-charge weapon, and insert the 0.020 inchFire gage. The firing pin assembly shallbe released on the first impulse of the firingmechanism.

4.3.9 High pressure test .

4.3.9.1 Each assembled machinegun, andthose spare parts for which proof firing isprescribed on the applicable drawings, shall

be subjected to the firing of one Governmentstandard high pressure proof cartridge undersupervision of the inspector.

4.3.9.2 Unless otherwise specified, suitable

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fixtures necessary for proof firing shall beprovided by the contractor.

4.3.9.3 Immediately after proof firing ac-

ceptance, proof marks shall be applied asindicated on the applicable drawings.

4.3.10 Function firing test. Machinegunsshall be tested for functioning as follows:each machinegun shall be fired 50 roundsright side feed and 50 rounds left side feedand, in addition, each machinegun shall befired a 10-round burst right side feed and a10-round burst left side feed for belt pulltest. The 10-round metallic linked belts shallbe loaded with 10-rounds of live and 2 roundsof dummy ammunition. The live ammunition

shall feed into the machinegun first. Con-nected to the rear of the link belt shall bea flexible connection extending over a freerunning pulley and connected to a pendenthelically wound compensating spring (Draw-

ing A5153086) to which is attached a 20-

pound w-eight. The pulley shall be so locatedthat the metallic linked belt will feed intothe gun horizontally or with not over 5 risefrom the pulley to the feedway.

4.3.10.1 When consistent satisfactory pro-duction has been proven the 50 round left

side feed test may be eliminated when au-thorized by the procuring agency.

4.3.11 Cyclic rate of fire test. Each ma-chinegun shall be fired 50 rounds continuousfire and the cyclic rate of fire recorded.

4.3.12 Targeting firing test. Using an ap-proved fixed rest fastened to a suitable base,not less than 5 guns from each lot of heavybarrel flexible and fixed machineguns shallbe targeted in accordance with the targetingdiagram shown on the applicable drawing.

4.3.13 Accuracy firing test. Using an ap-proved fixed rest fastened to a suitable base,not less than 5 machineguns from each lotshall be fired for accuracy requirements inaccordance with the applicable drawing.

4.3.14 Endurance test.

4.3.14.1 One machinegun selected by theinspector from each lot, found satisfactoryin other tests, shall be considered as a repre-sentative weapon and shall be subjected toa 10,000 round endurance test.

4.3.14.2 The firing schedule throughout the

test shall be 50 rounds spasmodic fire, fol-lowed by a 50 round continuous burst. The

barrel shall be cooled by injection of com-pressed air into the bore after each 100rounds. The average cyclic rate of fire shallbe taken and recorded on the last burst ofeach 500 rounds. The average cyclic rate offire for the endurance test shall be as speci-fied in 3.11. The direction of feed shall bechanged after every 500 rounds of firing.The machinegun shall be cleaned, oiled, andinspected after each 1,000 rounds and at theclose of a days firing, but no component shallbe altered or replaced, except that compo-nents broken or worn to the extent that theyare unserviceable shall be replaced. At leasttwo barrels shall be used in the endurancetest but not more than 5,000 rounds shall befired in any barrel.

4.3.14.3 Unless otherwise specified, endur-ance tested machineguns shall be scrapped.

4.3.15 Barrel erosion test.

4.3.15.1 Sample. From each lot of machine-guns and spare barrels a sample of barrelsshall be selected by the inspector for erosiontesting. Unless otherwise specified, barrelsselected for erosion testing shall be forwardedto Springfield Armory.

4.3.15.2 Procedure. Each barrel selectedfor erosion testing shall be fired as specifiedin procurement documents, or, in the ab-sence of specific requirements therein, asspecified by Springfield Armory.

4.4 Reinspection and retests.

4.4.1 Hangfires and misfires. If hangfires

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and misfires occur during any of the tests,the machinegun shall be subjected to thefiring pin indent test; and in the event thatthe firing pin blow is not within the speci-fied limits, the machinegun shall not be ac-cepted until properly corrected.

4.4.2 Malfunctions not attributable to

weapon. Malfunctions in any test assignableto improper linking of ammunition, improperfeeding of ammunition up to weapon, or de-fective ammunition, links or test equipment,shall not count against the machinegun be-ing tested.

4.4.3 Rejections. Components or assembliesrejected individually or by lots because ofinspection or any test except the interchange-

ability and endurance tests may be condi-tioned and resubmitted for inspection or testin which failure occurred and such other in-spection and tests deemed necessary by theGovernment inspector.

4.4.4 Interchangeabil ity retest . If the ma-chinegun representing any lot fail to meetthe specified requirements in the interchange-ability test, the lot shall be subject to retestof double the number of machineguns aswere in the original test.

4.4.5 Endurance retest . If the machine-gun representing any lot fails to meet thespecified requirements in the endurance test,

a retest shall be made, unless in the opinionof the inspector the failure indicates seriousdefects in the machineguns, in which caseretest shall be made only if authorized by theprocuring agency. In case a retest is made,the inspector shall select another machine-gun for the purpose from the lot under con-sideration. If a retest is not made or the ma-chinegun selected therefor fails in the retest,the lot shall be rejected subject to condition-

ing and further test.

5. PREPARATION FOR DELIVERY

5.1 Machineguns and spare parts shall beprepared for shipment in accordance with

MIL-G-1298A

packaging instructions cited on Drawings51-70-1A, 51-71-1A, or 51-119-1A, as ap-

plicable.

6. NOTES

6.1 Ordering data. Procurement documentsshould specify the following:

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

Title, number, and date of thisspecification.

Type of machinegun desired. (See1.2.)

Marking, if different. (See 3.1.2.)

List of interchangeable componentsand assemblies. (See 3.6. )

Requirements for erosion testing ofbarrels. (See 3.15.)

Type of ammunition to be used intest firing. (See 4.3.1.1. )

Number of preproduction andmonthly samples of guns andparts required. (See 4.3.6.4. )

Place of inspection. (See 6.2.1.)

Contractors responsibility in con-nection with tests. (See 6.2.2. )

6.2 Suggested contractual features.

6.2.1 Place of inspection. unless otherwisedeemed necessary, place of inspection shouldbe at the plant of the prime contractor.

6.2.2 Contractors responsibility. Unlessotherwise specified, all tests prescribed here-in should be performed by the contractorunder supenision of a Government inspector.

Notice.-This specification, together with specifica-tions and drawings pertaining to it and bearing a

Notice of similar restrictions, is intended for useonly in connection with procurement by the UnitedStates Government; and shall not be reproduced

either wholly or in part except when authorized inconnection with Government procurement nor be usedfor any other purpose except when specificallyauthorized by the Chief of Ordnance.

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