The CMMG Barrel and BCG Kit combines an 8-inch 5.7x28mm barrel with a bolt designed for CMMG’s Radial Delayed Blowback operating system. It is designed for assembly into a Mk4 or mil-spec AR-15 upper and is compatible with a CMMG Mk57 lower receiver or a Mk4/AR-15 mil-spec lower receiver when used with CMMG 5.7 AR conversion magazines. The supplied product information states that it cannot be shipped directly to California.

Key Specifications

• The chambering is 5.7x28mm for compatible AR platforms.
• The barrel measures 8 inches in length.
• The barrel uses 4140 chrome moly steel construction.
• The finish is listed as black matte with a salt bath nitride treatment.
• The barrel has 1/2×28 threading at the muzzle.
• The rifling uses a 1:9 twist rate.
• The profile features a medium taper.
• The operating system uses a Radial Delayed Blowback bolt.
• The kit includes the barrel and bolt.
• The configuration requires an enlarged ejection port for reliable operation.

For builders assembling a compatible 5.7x28mm AR platform, this kit brings the barrel and bolt components together in one purpose-specific configuration. Its threaded 8-inch barrel, medium-taper profile, and Radial Delayed Blowback design provide a straightforward foundation for a compatible upper assembly.