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10-10-2012, 7:31 PM

10-10-2012, 7:34 PM
M16 bolts are heavier and provide a more reliable cycling gun. IIRC most uppers ship with M16/auto bolts... I know my upper is mil-spec with an auto bolt. It's not a forbidden part.

10-10-2012, 8:44 PM
I'm assuming that you mean auto and semi from different manufacturers. Actual BCM bolt carrier groups do not come in semi, inlu auto. In terms of the difference between the two, its the carrier that's different. For auto, the top rear portion is the same in length as the bottom rear portion to the cutout while for semi the bottom rear is shorter vs the top portion to the cutout. Because that material from the bottom is missing, a semi-auto carrier will not properly trip the sear release on an actual full auto gun.

It's perfectly legal to use a full auto carrier. There are many other parts that make a rifle full auto, not just the carrier. As long as you don't have those other parts, you're GTG.