M16-Cut BCG Requirement for the MARC — FRT BCG Guide
The MARC requires an M16-profile bolt carrier group — commonly sold as a "full-auto-cut" or "M16-cut" BCG. This is a parts-geometry requirement, nothing more: an M16-profile carrier is a standard, legal, off-the-shelf AR-15 part, and it does not change how the MARC functions legally. The MARC family is ATF-determined lawful — one discharge per trigger pull.
Why the M16 profile is required
The MARC's cam lever is actuated by the underside of the bolt carrier as it cycles. An M16-profile carrier has a full-diameter rear shroud and full lug underneath; that geometry is what the cam lever rides on for correct timing. Semi-auto-profile carriers have that material milled away, so the lever isn't driven correctly through the cycle.
The carrier's full shroud also matters for safety timing: on an AR-15 bolt, the firing pin cannot reach the primer until the bolt is in battery. Correct carrier geometry keeps hammer timing where it belongs.
How to check what you have
Look at the bottom rear of the carrier:
- M16 profile: full-diameter steel all the way to the rear of the carrier; the firing-pin collar is fully shrouded.
- Semi-auto profile: a visible flat/relieved section milled out of the bottom rear.
Most quality BCGs sold today are M16 profile — check the listing for "M16" or "full-auto profile." If your carrier is semi-auto cut, replace the carrier; no modification to a semi-auto carrier is supported.
The rest of the build
An M16-cut BCG is one of three hardware requirements. Confirm the other two:
Then check your trigger on the compatibility chart.