MIL-DTL-001298D (AR)
3.2 Conformance inspection. Unless otherwise specified, all M2's shall be subjected to
conformance inspection in accordance with Table II and 4.3.
3.3 Sear engagement. The cocking lever, when operated by hand, shall retract
the firing pin assembly sufficiently to insure engagement of the firing pin extension
hook to the sear hook.
3.4 Firing pin protrusion. The firing pin protrusion shall not be less than 0.072 inch
and not more than 0.079 inch when measured from the bolt face.
3.5 Headspace. Each machine gun shall be capable of being adjusted for proper
headspace. With the bolt retracted until the barrel extension and the trunnion block are
separated approximately 1/16 inch, the distance between the rear face of the barrel and the
face of the bolt shall not be more than 0.206 inch and not less than 0.202 inch. This
adjustment is essential for proper weapon function and must be maintained during all firing
schedules.
3.6 Timing. After having been adjusted for headspace, each machine gun must then be
timed. The firing pin shall not release upon actuation of the triggering mechanism when the
gap between the barrel extension and the trunnion block exceeds 0.116 inch. However, at some
point in the interval where the gap between the barrel extension and the trunnion block is not
more than 0.116 inch and not less than 0.020 inch, the firing pin shall release upon actuation of
the triggering mechanism. This setting must also be maintained during subsequent firing
schedules.
3.7 Firing pin release. The firing pin shall be released by a load not exceeding 38
pounds applied to the sear slide and by a load not exceeding 26 pounds applied to the sear.
3.8 Firing pin indent. The firing pin indent shall be within the range of 0.017 to
0.040 inch and shall not be off center more than one-half the diameter of the indent.
3.9 High pressure resistance. Each M2 shall withstand the firing of one Government
standard caliber .50, M1 high pressure test cartridge. Bolt subassemblies, barrel extension
assemblies, and barrel assemblies shall be proof tested, inspected, and marked in accordance
with the applicable Drawings 6147463, 5504082, and 7265156. If components are proof
tested prior to assembly and then assembled into a complete machine gun the components
shall be re-proof tested and inspected with the complete machine gun.
3.9.1 Magnetic particle inspection. All parts of the M2 shall be free of cracks,
seams, or other defects after proof firing. The bolt subassembly, barrel extension assembly,
barrel assembly, and receiver assembly of each M2 shall be magnetic particle inspected and
proof marked as specified on the applicable Drawings 6147463, 5504082, 7265156, and
6535480. Those assemblies which receive a second proof test shall be marked with a prefix
"2" at the location of the previous proof marking.
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