MIL-C-70599A(AR) 20 January 1994 SUPERSEDING MIL-C-70599(AR) 01 APRIL 1987 MILITARY SPECIFICATION CARBINE, 5.56MM: M4 This Specification is approved for use by the US Army Armament Munitions and Chemical Command and is available for use by all Departments and Agencies of the Department of Defense. 1. SCOPE 1.1 Scope. This specification covers the requirements, examinations and tests for a 5.56mm lightweight, air-cooled, gas operated, magazine-fed carbine designed for either three shot automatic burst or semi-automatic fire (see 6.1). 2. APPLICABLE DOCUMENTS 2.1 Government documents. 2.1.1 Specifications, standards and handbooks. The following specifications, standards and handbooks form a part of this document to the extent specified herein. Unless otherwise specified, the issues of these documents are those listed in the issue of the Department of Defense Index of Specifications and Standards (DoDISS) and supplement thereto, cited in the solicitation (see 6.2). SPECIFICATIONS MILITARY MIL-P-116 - Preservation, Methods of MIL-C-372 - Cleaning Compound, Solvent MIL-W-13855 - Weapons: Small Arms and Aircraft Armament Subsystems, General Specification for MIL-I-45607 - Inspection Equipment, Acquisition, Maintenance and Disposition of Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document, should be addressed to: Commander, U.S. Army ARDEC, ATTN: SMCAR-BAC-S, Picatinny Arsenal, New Jersey 07808-5000 by using the Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter. AMSC N/A FSC 1005 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. MIL-C-70599A(AR) MIL-L-46000 Lubricating Oil, Semi-Fluid (Automatic Weapons) MIL-C-46936 - Cartridge, 5.56mm, Test, High Pressure, M197 MIL-W-63150 Weapons and Support Material, Standard Quality Assurance Provisions for MIL-L-63460 Lubricant, Cleaner and Preservative for Weapons and Weapon Systems MIL-C-63989 Cartridge, 5.56mm, Ball M855 MIL-A-70625 Automated Acceptance Inspection Equipment for Non-Electronic Components, Design, Testing and Approval of STANDARDS MILITARY MIL-STD-109 - Quality Assurance Terms and Definitions MIL-STD-1949 Inspection, Magnetic Particle MIL-STD-45662 - Calibration System Requirements (Unless otherwise indicated, copies of federal and military specifications, standards, and handbooks are available from DODSSP - Standardization Documents order Desk, 700 Robbins Avenue, Bldg. 4D, Philadelphia, PA 19111-5094. ) 2.1.2 Other Government documents, drawings and publications. The following other Government documents, drawings and publications form a part of this document to the extent specified herein. Unless otherwise specified, the issues shall be those cited in the solicitation. DRAWINGS (see 6.9) U.S. ARMY ARMAMENT RESEARCH, DEVELOPMENT AND ENGINEERING CENTER (ARDEC) PRODUCT DRAWINGS 9342868 - Cartridge, 5.56MM, Ball; M855 9390000 - Carbine, 5.56MM: M4 PACKAGING DRAWINGS SPI9390000 - Special Packaging Instructions for M4 Carbine INSPECTION EQUIPMENT DRAWINGS 8440218 - Gage, Indicator 8440219 - Gage, Plug 8440220 - Gage, Plug 8440920 - Cylinder, Pressure 2 MIL-C-70599A(AR) 8443733 - Gage, Plug, Straightness 8443915 - Gage, Headspace (Min) 8443949 - Gage, Headspace (Max) 8443957 - Gage, Location 11037922 - Gage, Indicating 11837944 - Barrel and Bolt Proof Testing Fixture 11838443 - Gage, Flush Pin (Copies of other Government documents, drawings, and publications required by contractors in connection with specific acquisition functions should be obtained from the contracting activity or as directed by the contracting activity.) 2.3 Order of Precedence. In the event of a conflict between the text of this document and the references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. (See contract provisions for additional precedence criteria). 3. REQUIREMENTS 3.1 First article. When specified in the contract or purchase order (see 6.2), a sample shall be subjected to first article inspection in accordance with the technical provisions herein (4.4). Unless otherwise specified (see 6.2), the first article shall include the pilot pack (see 5.1). 3.2 Materials and construction. Carbines and parts shall conform to the materials and construction requirements specified herein, on Drawing 9390000 and drawings applicable thereto, and be in accordance with the applicable materials and construction provisions of MIL-W-13855. 3.3 Design. Carbines and parts shall conform to the design specified herein, on Drawing 9390000 and drawings applicable thereto, and be in accordance with the applicable design provisions of MIL-W-13855. 3.3.1 Upper receiver and lower receiver groups. The upper receiver group shall be attached to he lower receiver group by the pivot pin and shall be held securely in the closed position by the takedown pin. When the takedown pin and pivot pin are withdrawn to the stop position, the upper receiver group shall disassemble from the lower receiver group. 3.3.2 Lower receiver group. 3.3.2.1 Hammer. The hammer shall pivot on the hammer pin throuqh its full range of travel without binding, and when the hammer is released from the cocked position, it shall pivot forward to the stop position under spring action. 3 MIL-C-70599A(AR) 3.3.2.2 Automatic sear. The automatic sear shall be retained in the lower receiver by the automatic sear pin. The automatic sear shall move through its full range of travel under spring tension without binding, and shall engage and restrain the hammer when the fire control selector is in the “BURST” position and the hammer is cocked by the bolt carrier. The automatic sear shall restrain the hammer until the sear is tripped by the forward motion of the bolt carrier. 3.3.2.3 Fire control selector. The fire control selector shall have three positions; safe, semi-automatic and burst and shall rotate manually without binding from one position to another when the hammer is cocked. The selector shall remain in place in each position by perceptible spring detent load until manually reset and shall be retained in the lower receiver by a spring loaded detent. With the hammer cocked, when the selector iS placed in the “SAFE” position, it shall prevent the trigger from releasing the hammer so that the carbine is incapable of being fired. When the selector is placed in the “SEMI-AUTOMATIC” position, it shall permit the disconnect to engage the hammer, so that the carbine is capable of semi-automatic firing only (single shot with each pull of the trigger). When the disconnect has engaged the hammer and the trigger iS released, the disconnect shall release the hammer without the hammer falling. When the selector is placed in the “BURST” position, it shall permit the automatic gear to engage the hammer, so that the carbine is capable of burst firing. (One, two, or three continuous shots the first time the trigger is pulled and held back. Three continuous shots on the second and each successive time the trigger is pulled and held back. One, two, or three shots if the trigger is released before completion of the three shot cycle or all cartridges are expended before completion of the three shot cycle.) 3.3.2.4 Bolt catch. The bolt catch shall be retained on the lower receiver by the spring pin and held in the “down” position by the bolt catch plunger and spring. The bolt catch shall move through its full range of travel without binding and when positioned manually or by action of the magazine follower, it shall remain engaged and hold the bolt in the open (rearward) position. When the bolt catch is depressed the bolt shall return to battery position. When a fully loaded magazine is inserted into the magazine well and the bolt catch is depressed, the bolt shall return to battery position, stripping a cartridge from the magazine, and cambering it. 3.3.2.5 Magazine catch and magazine release button. The magazine catch, under spring action, shall securely retain the magazine in the magazine well. The magazine release button, when depressed, shall disengage the magazine catch from the magazine and permit removal of engagement with the magazine. When the bolt is held open (rearward) by the bolt catch, and the magazine release button is depressed, the empty magazine shall be ejected 4 MIL-C-70599A(AR) under spring assist from the magazine follower being depressed by the bolt-catch. The spring tension of the magazine catch shall be adjustable by depressing the magazine release button and rotating the magazine catch clockwise to tighten; counterclockwise to loosen. The magazine release button shall be assembled to the magazine catch shaft, such that the end of the shaft is within one turn of being flush with the face of the magazine release button. 3.3.2.6 Disconnects. 3.3.2.6.1 Semi-disconnect. The semi-automatic disconnect shall pivot freely on the trigger pin under spring action. When the selector iS in the semi-automatic position, the semi- disconnect shall engage and restrain the hammer in the cocked position until the trigger is released. When the trigger its released, the disconnect shall allow the hammer to return to the normal cocked position. 3.3.2.6.2 Burst disconnect. The disconnect shall pivot freely on the trigger pin under spring action. When the selector is in the burst position, the burst disconnect shall engage and restrain the hammer in the cocked position every third shot until the trigger is released. When the trigger is released, the disconnect shall allow the hammer to return to the normal cocked position. 3.3.2.7 Trigger. The trigger shall hold the hammer in the cocked position until the trigger is pulled. After partial or completed trigger pull, the trigger shall return to its normal forward positions (cocked and uncocked) under spring action. 3.3.2.8 Trigger guard. The trigger guard shall pivot on the trigger guard pin through its full range of travel. The trigger guard shall be retained in the closed position by the trigger guard spring loaded detent, and when in the open position it shall remain open against the pistol grip without manual assistance. 3.3.2.9 Pivot pin and takedown pin. The pivot pin and takedown pin shall move through their full range of travel without binding, and shall be retained in the extreme in-and-out position by spring action of the detents. 3.3.2.10 Pistol grip. The pistol grip shall be securely attached to the lower receiver and shall not interfere with operation of the selector lever. 3.3.2.11 Buttstock assembly. The buttstock assembly shall be free to slide on the lower receiver extension between the extended and retracted position. Pressure on the release lever (rear end) towards the buttstock shall withdraw the lock pin allowing movement from one position to the other. Release of the 5 MIL-C-70599A(AR) lever when the buttstock is positioned in the extended or retracted position shall allow the lock pin to secure the buttstock in position. Pulling the rear end of the release lever away from the buttstock shall allow the buttstock to slide rearward off the lower receiver extension. 3.3.2.12 Buffer assembly. The buffer assembly shall function through its full range of travel under spring action without binding. The buffer assembly shall be securely retained in the lower receiver assembly by the spring loaded buffer retainer and be capable of being disassembled from the lower receiver assembly when the retainer is manually depressed. 3.3.2.13 Receiver extension. The lower receiver extension shall be securely fastened to the lowere receiver by means of the receiver end plate being staked to the receiver extension nut. The receiver shall not rotate from its correct position with the release lever in the 6 o'clock position on the vertical centerline. 3.3.3 Upper receiver group. 3.3.3.1 Barrel assembly. The barrel shall be free of cracks, seams and other injurious defects and the bore and chamber shall be free of pockets, rings, bulges and other deformations. The chromium plating in the chamber and bore shall be free of nodules, flaking, pits, stripping, anode burns and evidence of etched base steel. Burrs and sharp edges shall be removed from chamber edges, and bolt locking lugs. Scratches of marks occurring in a chamber which otherwise meets the surface roughness requirements, shall be permitted, provided they do not cause marks on the cartridge case of high pressure test cartridge fired in the chamber. 3.3.3.1.1 Barrel assembly straightness. The barrel assembly shall be straight to the extent that a cylindrical plug with a diameter of .2173 + .0001 inches, and six (6) inches in length must drop through the barrel bore of its own weight. Also, a self aligning plug inserted three (3) inches into the barrel bore at the muzzle, shall have a maximum angular deviation from the theoretical axis of zero degrees and three minutes (0°3’). 3.3.3.2 Gas tube. The gas tube shall be securely retained to the front sight assembly by the gas tube spring pin. The gas tube shall be free of mutilations and positioned for proper alignment with the bolt carrier key. 3.3.3.3 Handguard. The two-piece handguard shall be held firmly in place by the handguard cap and the spring loaded slip ring in the barrel nut assembly. When the slip ring is depressed rearward the handguards shall be capable of being removed. 6 MIL-C-70599A(AR) 3.3.3.4 Front sight. The front sight shall be securely attached to the barrel assembly by two taper pins. The front sight post shall be held in position by the spring loaded front sight detent. The detent, when depressed, shall disengage the front sight post and allow vertical adjustment of the post. Clockwise rotation of the front sight post, as indicated by the arrow on the top of the front sight, shall lower the front sight post. When the carbine is zeroed as specified in 3.4.6, there shall be at least 16 additional clicks of adjustment available in a downward direction. The front sight shall provide a means for retaining and positioning a bayonet knife. 3.3.3.5 Rear sight. The rear sight shall pivot to full vertical position of both normal and short range peeps and be held in each position under spring action when at the extreme left and extreme right windage positions. The windage knob shall be held in position by the spring loaded detent. The windage knob shall be capable of rotating seven complete revolutions, moving the rear sight from the extreme left to the extreme right without binding. The rear sight shall also be capable of and calibrated for elevating, by means of an elevation knob, to compensate for trajectory for ranges from 300 meters to 800 meters. The 0-200 meter setting shall be accomplished by setting the elevation knob on 300 meters and “flipping-up” the close range rear sight peep. The rear sight shall be adjusted as specified in 3.4.6. 3.3.3.6 Ejection port cover. The ejection port cover shall operate through its full range of travel under spring action without binding. The cover shall be retained in the closed position by the cover detent, and shall open under spring action when the bolt carrier is moved from the locked position rearward, or from the open position forward. 3.3.3.7 Forward assist assembly. The forward assist assembly shall operate through its full range of travel without binding. When depressed and released, it shall return under spring action to a fully outward position with the pawl completely disengaged from the bolt carrier. Depressing and releasing the forward assist shall cause progressive movement of the bolt carrier assembly into the battery position. 3.3.3.8 Compensator. The compensator shall be fastened securely to the barrel in accordance with the applicable drawings. 3.3.3.9 Front sling swivel. The mount (sling) swivel shall be securely retained on the barrel (between the two front sight legs) by the locking bar and spring pins. The gun sling swivel shall be securely fastened to the mount swivel by the pin. 3.3.4 Bolt carrier group. 7 MIL-C-70599A(AR) 3.3.4.1 Key and bolt carrier assembly. The bolt carrier and key assembly shall move through its full range of travel without binding in the upper receiver. The carrier key shall engage the gas tube freely when the bolt carrier moves in the forward position. The bolt carrier key screws shall be torqued and staked in accordance with the applicable drawings. 3.3.4.2 Firing Pin. The firing pin shall be retained in the bolt and bolt carrier assembly by the retaining pin. The firing pin shall move freely through its full range of travel in the bolt carrier assembly. The firing pin protrusion shall be a maximum of .036 inches and a minimum .028 inches. The chromium plating of the firing pin shall be free of nodules, flaking, stripping, anode burns and evidence of etched base steel, except as specified on the applicable drawing. 3.3.4.3 Charging handle. The charging handle shall move freely through its full range of travel in the upper receiver. When the charging handle is placed in the forward position it shall engage and lock securely in the upper receiver. 3.3.4.4 Bolt assembly. The bolt assembly shall be retained in the bolt carrier by the bolt cam pin and shall move through its full range of travel. The cam pin hole shall be swaged in accordance with the applicable drawings to prevent improper assembly of the bolt cam pin in the bolt assembly. 3.3.4.4.1 Extractor. The extractor shall be retained in the bolt by the extractor pin. The extractor shall move through its full range of travel under spring action without binding in the bolt and shall be capable of engaging and extracting cartridge cases from the barrel chamber when the carbine is function fired or manually operated. 3.3.4.4.2 Ejector. The ejector shall be retained in the bolt by the ejector pin and shall be held in the forward position by the ejector spring. The ejector shall move through its full range of travel under spring action without binding in the bolt and shall eject cartridge cases completely out of the carbine when the carbine is function fired or manually operated. When fully depressed, the ejector pin shall be flush with or below the cartridge seat in the bolt. 3.3.4.4.3 Cam pin. The cam pin shall be retained in the bolt assembly by the firing pin. The cam pin shall move through its full range of travel in the bolt carrier without binding. The cam pin shall be capable of being removed from the bolt carrier without removal of the bolt carrier key assembly. The cam pin shall be capable of being disassembled from the bolt and bolt carrier assembly and reassembled 180° about its vertical axis from its original position without causing binding in the assembly. 8 MIL-C-70599A(AR) 3.4 Performance characteristics. 3.4.1 Headspace. The headspace shall not be less than 1.4646 inches nor more than 1.4706 inches when measured to the .330 inch datum diameter on the first shoulder of the chamber. 3.4.2 Firing pin indent. When the bolt is closed and the firing mechanism is released, the firing pin indent shall not less than 0.020 inch. The firing pin indent shall not be off- center more than one half the maximum diameter of the indent. When, in a vertical, muzzle down position, the bolt carrier assembly is released from the full recoil position and the firing mechanism is not actuated, the firing pin indent shall not be more that 0.008 inch. 3.4.3 Trigger pull. The trigger pull shall be free of creep and shall be within the range of 5.5 to 9.5 pounds. Creep shall be interpreted to mean any perceptible rough movement between the time the trigger slack is taken up and the hammer is released. After partial or complete trigger pull, the trigger shall return to its normal forward position (cocked and uncocked) under spring action. 3.4.4 High Pressure resistance. Each barrel assembly and bolt shall withstand the firing of one Government standard M197, 5.56mm high pressure test cartridge conforming to MIL-C-46936. After proof firing, parts shall be free of cracks, seams and other injurious defects as evidenced by visual and magnetic particle inspection. 3.4.5 Functioning. Each carbine shall operate without malfunctions or unserviceable parts. The cyclic rate of fire for a 3 round burst using a 30 round magazine shall be within 700 to 970 rounds per minute when firing Government standard M655, 5.56mm ball cartridges conforming to MIL-C-63989. 3.4.6 Targeting and accuracy. A series of 10 rounds fired from each carbine at a range of 91.4 meters shall be within the extreme spread and targeting area (heavy outline) specified in Figure I when the front and rear sights are set as follows. The normal rear sight peep (sight rotated fully rearward) shall be used with the rear sight set centrally in the slot for windage within plus or minus five (5) clicks. The top edge of the front sight post flange shall be set flush to .030 inch below the bottom surface of the front sight slot. Ammunition shall be Government standard M855, 5.56mm ball cartridges conforming to Drawing 9342868 and shall have been certified by the Government to be of a quality that will have an average horizontal and vertical standard deviation of 3.4 inches to 4.0 inches at 600 yards as measured in accordance with MIL-C-63989. 9 MIL-C-70599A(AR) FIGURE I. Targeting and accuracy diagram. 10