CMMG 57D0476 Replacement Barrel Kit w/ BCG 5.7x28mm 16.1" Threaded - Black Salt Bath Nitride

The CMMG 57D0476 is a complete 5.7x28mm barrel and bolt carrier group kit built for the AR-platform. Designed to drop into a Mk4 / Mil-Spec AR-15 upper receiver, this kit lets a shooter build or convert an AR-platform firearm to the high-velocity 5.7x28mm cartridge using a CMMG Mk57 lower receiver or any standard Mk4 / AR-15 Mil-Spec lower when paired with CMMG 5.7 AR Conversion Magazines.

The barrel is a 16.10" threaded profile cut from 4140 Chrome Moly steel and finished in Salt Bath Nitride for a durable, corrosion-resistant matte black surface. The matched bolt carrier group uses CMMG's signature Radial Delayed Blowback operating system, purpose-engineered to safely handle the high pressures of the 5.7x28mm cartridge in an AR-platform format.

This is a genuine CMMG replacement and build component - the barrel and BCG are sold together as a matched set and are intended to be assembled into a host upper receiver. Whether you are building a new 5.7x28mm AR from the ground up or converting an existing lower, the 57D0476 kit provides the critical operating components in one package.