CMMG 8in Barrel & BCG Kit — 5.7x28mm

This CMMG kit includes an 8-inch barrel and matching bolt/BCG configured for 5.7x28mm to assemble into a mil-spec AR-15 upper. It uses CMMG’s Radial Delayed Blowback operating system to reduce bolt mass and aid in controllability compared with straight blowback designs. The barrel is 8 inches with a 1:9 twist and a corrosion-resistant salt-bath nitride finish in black. The kit is intended for use with CMMG Mk57 lowers or standard Mk4/AR-15 lowers when combined with CMMG 5.7 conversion magazines.

Key Specifications

• The caliber is 5.7x28mm.
• The barrel length is 8 inches.
• The barrel material is 4140 chrome-moly steel.
• The finish is salt-bath nitride (black matte).
• The twist rate is 1:9.
• The muzzle is threaded 1/2"-28 for muzzle devices or suppressors.
• The operating system is Radial Delayed Blowback.
• The kit includes bolt and barrel for straightforward assembly.
• The design requires an enlarged ejection port and porting for reliable operation.
• Sights are none (no fixed sights included).

Engineered for builders who want a compact 5.7x28mm AR pistol or SBR, this CMMG barrel and BCG kit delivers a turnkey core with features that support reliable function and straightforward installation into mil-spec uppers. The combination of a salt-bath nitride 4140 barrel, threaded muzzle, and the Radial Delayed Blowback bolt provides a compact, serviceable foundation for a high-performance short-barrel 5.7x28mm platform.