CMMG Replacement Barrel Kit Features The CMMG Replacement Barrel Kit gives an AR-15 or MK4 upper everything needed to run dedicated .22 LR ammunition with just a magazine left to add. The 4.5 medium taper profile barrel is machined from 4140 chrome moly steel and finished with a black nitride salt bath treatment inside and out for corrosion resistance and smooth function. A 1:16 twist rate is matched to the lighter bullet weights typical of .22 LR ammunition and the sporting chamber is cut specifically for reliable rimfire feeding. The barrel is threaded 1/2x28 leaving the option open for a suppressor or muzzle device on the dedicated rimfire upper. Included in the kit is a bolt carrier group sized and built for the .22 LR conversion taking the guesswork out of matching components for reliable cycling. CMMG recommends a round style hammer rather than a notched hammer since notched hammers can cause function issues with this conversion. The manufacturer also notes that 36 grain plated nose bullets have proven to be the most reliable choice for consistent cycling. Once installed the CMMG Replacement Barrel Kit turns an existing AR-15 or MK4 upper into a low-cost low-recoil trainer that is ideal for practice plinking and teaching new shooters the platform. CMMG Replacement Barrel Kit Specifications Manufacturer: CMMG Model: Replacement Barrel Kit Compatible Hosts: AR-15 MK4 Caliber: .22 LR Barrel Length: 4.5 Barrel Material: Chrome Moly Steel Barrel Finish: Black Nitride Barrel Description: Threaded Medium Taper Profile Twist Rate: 1:16 Thread Pattern: 1/2x28 Includes: Bolt Carrier Group Sights: None Available At: GrabAGun