Glad to hear your carbine headspaces correctly.
From the 1994 M4 MIL-SPEC ( http://biggerhammer.net/ar15/milspec...71186_(AR).pdf )
and how they check: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.
3.4.4 Hiqh 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.The focus now goes back to barrel and/or your ammo.4.7.1.1 Minimum gage. The bolt shall be moved rearward to the open position. The minimum headspace gage shall be inserted in the chamber and the bolt shall be returned to the battery position. Only finger pressure shall be applied to close the bolt. To be acceptable the bolt shall fully close.
4.7.1.2 Maximum gage. The bolt shall then be retracted to the open position and the minimum headspace gage removed from the chamber. The maximum headspace gage shall be inserted in the chamber and the bolt returned to the battery position. Only finger pressure shall be used to close the bolt. To be acceptable the bolt shall not fully close.
4.7.1.3 Dimensional inspection. If the above results are in dispute, the carbine shall disassembled and the 1.6206 + .0030 barrel dimension and the .15: - .003 bolt dimension shall be measured to determine compliance with the drawing requirements.


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