The Colt bolt carrier group — the mil-spec BCG used in Colt M4A1 and M16 production, available with or without Colt "C" carrier markings.
Colt bolt carrier groups are the standard against which mil-spec BCGs are measured. The bolt is forged from Carpenter 158 steel — the alloy specified in the M16/M4 Technical Data Package — and is magnetic particle inspected (MPI) and high-pressure proof tested (HPT) at the factory. The carrier is machined to full-auto profile dimensions (the full-mass carrier required for reliable cycling in M4A1-pattern rifles) with a chrome-lined gas key bore and properly staked gas key.
Current-production Colt BCGs come in two marking configurations. Some carriers bear the Colt "C" roll-mark or MPC/MPC-2 markings on the bolt — these are from serialized production runs and are preferred by builders who want visible Colt provenance. Other current-production Colt BCGs ship with a characteristic white dot on the bolt and no external markings on the carrier. Both are genuine Colt production with the same metallurgy and inspection process. The choice is cosmetic for a functional build, but matters for clone-correct builders who need era-appropriate markings.
For clone-correct builds — SOPMOD Block I, Block II, URG-I, Mk18, or any M4A1-pattern rifle — a Colt BCG is the program-correct bolt carrier group. Aftermarket BCGs from other manufacturers may meet or exceed the mechanical spec, but they are not Colt, and the roll-marks tell the story on a clone build.
We use Colt BCGs in our own builds here at Charlie's. If it's good enough for the rifles we ship, it's good enough for yours. Grab one while we have them — Colt releases these to the commercial market in batches.
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