MIL-DTL-63997C
the time the trigger slack is taken up and the hammer is released.
3.6.3 High pressure resistance.
3.6.3.1 High pressure resistance test. The barrel assembly in accordance with drawing
9349054 and bolt in accordance with drawing 8448510 shall withstand the firing of one M197,
5.56mm high pressure test cartridge in accordance with drawing 10533839 or commercial
equivalent conforming to SAAMI-Z299.4 specifications. Unless otherwise specified, the barrel
assembly and bolt shall be tested concurrently.
3.6.3.2 Headspace. After the high pressure resistance test, each weapon shall be gaged to
meet headspace requirement after proof firing.
3.6.3.2.1 Minimum headspace. After the high pressure resistance test, the headspace
shall not be less than 1.4646 inches when measured to the 0.330 inches datum diameter on the
first shoulder of the chamber.
3.6.3.2.2 Maximum headspace. After the high pressure resistance test, the headspace
shall not be greater than 1.4706 inches when measured to the 0.330 inches datum diameter on the
first shoulder of the chamber.
3.6.3.3 Barrel assembly integrity. After the high pressure resistance test, the barrel
assembly shall be free of cracks, seams, or other defects.
3.6.3.4 Bolt assembly integrity. After the high pressure resistance test, the bolt assembly
shall be free of cracks, seams, or other defects.
3.6.3.5 High pressure test cartridge integrity. After the high pressure resistance test, the
cartridge cases shall be examined for bulges, splits, rings and other defects caused by defective
chambers of the barrel assembly.
3.6.4 Function firing.
3.6.4.1 Function firing semi-automatic. The weapon shall operate without malfunctions
or unserviceable parts (see 6.10.3), as defined by Table I, during one 30-round cycle in semi-
automatic mode. Rounds number 5 thru 15 shall be used for the target and accuracy verification
in support of 3.6.6.
3.6.4.2 Function firing burst. The weapon shall operate without malfunctions or
unserviceable parts, as defined by Table I, during one 30-round cycle in burst mode. The first
trigger pull shall fire one, two or three rounds. Each successive trigger pull shall fire three (3)
rounds as long as the trigger is held fully rearward during the entire three (3) round burst. The
last trigger pull when the magazine is emptied shall be a one, two or three round burst. The
fourth or fifth trigger pull shall be used for the cyclic rate of fire verification in support of cyclic
rate of fire (see 3.6.5).
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