CMMG Barrel and Bolt Group Kit 4.5inch MT 4140CM 22LR

The CMMG Barrel and Bolt Group Kit 4.5-inch MT 4140CM 22LR (model 22D5B6E) is a dedicated rimfire conversion system engineered to transform an existing AR-platform upper receiver into a .22 Long Rifle training and practice tool. Chambered in 22LR with a 1:16 twist rate, this kit delivers consistent accuracy across standard and match-grade ammunition while minimizing recoil and noise—critical advantages for extended range sessions, low-light training, and cost-effective marksmanship development.

The barrel features a medium taper profile constructed from 4140 chrome-moly steel and finished with salt bath nitride treatment inside and out, providing corrosion resistance and durability equivalent to military-grade AR barrels. The 4.5-inch length balances velocity with compact handling characteristics, while the 1/2-28 threaded muzzle accepts standard 22LR suppressors and flash hiders. The bolt group is purpose-built for rimfire operation, ensuring reliable feeding and extraction with magazine-fed 22LR ammunition. Salt bath nitride finishing protects both internal and external surfaces against rust and wear, critical for systems exposed to humid storage or field conditions.

This conversion kit is designed for shooters who want to extend the utility of their existing AR upper receiver without acquiring a separate platform. LEOs and military personnel use 22LR conversions for low-cost fundamentals training, dry-fire alternatives, and range time that preserves centerfire ammunition budgets. Competitive shooters leverage rimfire conversions for sight-in work and transition drills. The system requires only a 22LR-compatible magazine to be operational—a straightforward upgrade path for users already invested in AR infrastructure.

CMMG is recognized for precision rimfire conversion engineering and tight manufacturing tolerances. The medium taper profile and 4140 chrome-moly construction represent standard-tier barrel quality, appropriate for training and recreational use rather than match-grade accuracy demands. The salt bath nitride finish meets AR platform durability expectations and simplifies field maintenance.