MIL-DTL-63997C
deviation of zero degrees and three minutes (0° 3') from the axial centerline of the barrel.
3.5.2 Gas tube.
3.5.2.1 Gas tube retention. The gas tube shall be securely retained to the front sight
assembly by the gas tube spring pin.
3.5.2.2 Gas tube alignment. The gas tube shall be positioned for proper alignment with
the bolt carrier key. Proper alignment shall allow for the gas tube to freely move in and out of
the bolt carrier key without binding.
3.5.3 Handguard.
3.5.3.1 Handguard retention. 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.
3.5.3.2 Handguard removal. When the slip ring is depressed rearward the handguard
shall be capable of being removed.
3.5.4 Front sight assembly.
3.5.4.1 Front sight assembly retention. The front sight assembly shall be securely
retained on the barrel assembly by two taper pins.
3.5.4.2 Front sight post retention. The front sight post shall be held in position by the
spring loaded front sight detent.
3.5.4.3 Front sight post adjustment. 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 weapon is zeroed, there shall be at least 16 additional clicks of adjustment available in
a downward direction.
3.5.5 Rear sight.
3.5.5.1 Rear sight motion. The rear sight shall pivot to full vertical position of both
normal and short range peeps and be held under spring action when at the extreme left and
extreme right windage positions.
3.5.5.2 Rear sight windage knob position retention. The windage knob shall be held in
position by the spring loaded detent.
3.5.5.3 Rear sight windage knob motion. 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.
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