CMMG BOLT CARRIER GROUP M16 556

Description

The CMMG M16 Bolt Carrier Group is a complete, mil-spec replacement or build component designed for AR-platform rifles chambered in 5.56x45mm and .300 BLK. It suits builders and owners who want a drop-in group that meets military dimensional standards without having to source and assemble individual components.

The bolt is machined from 9310 steel, a nickel-chromium alloy chosen for its toughness under the repeated high-stress cycling that a bolt faces at the locking lugs and cam pin. The carrier uses 8620 steel, which offers the surface hardness needed to survive continuous friction against the upper receiver and buffer tube components while retaining enough core ductility to resist cracking. The extractor is cut from 4140 steel, a material that holds its spring-back characteristics over a high round count and resists the shear stress of stripping a case from the chamber under pressure.

All three components receive a Salt Bath Nitride finish. This is a ferritic nitrocarburizing process that diffuses nitrogen and carbon into the steel surface rather than depositing a coating on top of it, which means there is no meaningful change to the dimensions of critical surfaces. The result is a hard, corrosion-resistant layer that also reduces friction between the carrier and receiver during the cycling stroke — an advantage in dusty or wet conditions where a bare steel surface would need more frequent lubrication to maintain reliable function.

The M16 carrier profile is dimensionally larger than a standard AR-15 carrier in the area above the fire control group. In a semi-automatic host, this additional mass slows the unlocking cycle slightly and adds a small amount of inertia to the rearward stroke, which can smooth out felt recoil impulse compared to a lighter carrier. CMMG backs this group with their Lifetime Quality Guarantee.