CMMG Barrel Nut RKM AR15 Black. This provides a secure fit and ensures the barrel can rotate freely with no damage to the gas tube or the upper receiver. The collared design allows the shooter to exercise a degree of control over the closing velocity of the charging handle as the barrel is pushed forward. The barrel nut/barrel collar engages the charging handle gas port and prevents any movement or locking forward of the charging handle. Specifications for CMMG Barrel Nut RKM: Manufacturer: CMMG Color: Black Condition: New Gun Type: Rifle Package Contents: CMMG Barrel Nut RKM What firearm models does the manufacturer say CMMG Barrel Nut RKM is compatible with? The manufacturer says that CMMG Barrel Nut RKM is compatible with AR-15 CMMG Mk3CMMG 55DA244: Barrel Nut RKM AR15 Black