The CMMG Replacement Barrel Kit (brand part no. 22D5B6E) gives AR-15 and Mk4 upper owners everything needed to convert an existing upper to a dedicated .22 LR, chambering, with a 4.5-inch threaded barrel finished in Black Nitride over chromoly steel and a matching bolt carrier group. Once installed, all that’s left to add is a magazine before the upper is ready to run. CMMG recommends a round-style hammer for best performance, since notched hammers can cause function issues, and 36-grain plated round-nose bullets have proven to be the most reliable choice for cycling.

Key Specifications

• Converts an existing upper to .22 LR chambering.
• Barrel measures 4.5 inches in length.
• Threaded at the muzzle.
• Finished in Black Nitride.
• Constructed from chromoly steel.
• Rifled with a 1:16 twist rate.
• Includes a matching bolt carrier group.
• Built to fit the AR-15/Mk4 platform.
• Ships at approximately 1.19 lb.

Frequently Asked Questions

Does this kit include a bolt carrier group? Yes, a matching .22 LR bolt carrier group is included.

What ammunition works best in this conversion? 36-grain plated round-nose bullets have proven to be the most reliable choice.

Does this kit work with any hammer? Best performance requires a round-style hammer; notched hammers can cause function issues.

Buy the CMMG Replacement Barrel Kit

Turn your AR-15 or Mk4 upper into a dedicated .22 LR trainer. Order it from our CMMG lineup of AR15 build kits for fast shipping from our Lubbock, Texas gun shop.