CMMG 5″ Barrel & BCG Kit — 9mm, 4140 CM

Description

The CMMG 5″ Barrel and BCG Kit is a factory-configured solution for building a 9mm pistol-caliber carbine on the AR platform using CMMG’s Radial Delayed Blowback system. The kit pairs a 5-inch 4140 chrome moly barrel with a radial delayed blowback bolt carrier group to reduce mass and cyclic forces compared with traditional straight blowback designs. It is engineered to work with mil-spec AR-15 upper receivers that have a modified ejection port and with compatible lowers when used with 9mm AR conversion magazines.

Key Specifications

• The barrel length is 5 inches.
• The cartridge/chamber is 9×19 NATO (9mm).
• The barrel material is 4140 chrome moly.
• The barrel twist rate is 1:10.
• The barrel is threaded with 1/2-28 muzzle threads.
• The operating system is Radial Delayed Blowback.
• The kit weight is approximately 1.4 lbs.
• The kit includes the barrel and bolt/BCG.
• The design requires an enlarged ejection port for reliable operation.

Practical and engineered for builders who want a compact 9mm AR-style platform, this kit delivers the core components needed to assemble a reliable pistol-caliber carbine using CMMG’s RDB approach. Its 5″ 4140 barrel and purpose-built bolt provide a compact footprint and system-level compatibility for mil-spec upper receivers modified for radial delayed operation.