CMMG Barrel Sub-Assm 10.5in MT 4140CM Salt Bath Nitride 5.56mm. The 10.5 5.56mm barrel is no exception. Rest assured that all barrel sub-assemblies are properly headspaced and perfect for your next AR build. Specifications for CMMG AR 5.56mm 10.5in Barrel Sub-Assm: Manufacturer: CMMG Finish: Salt Bath Nitride Fabric/Material: 4140 Steel Caliber: 5.56x45mm NATO Barrel Length: 10.5 in Barrel Profile: Medium Tapered Gas System Length: Carbine Length Gas Block Journal Size-Diameter: .750 in Threads per Inch: 1/2x28 Barrel Twist Rate: 1-7 Flutes: No Gun Make: CMMG Weight: 0.9 lb Package Contents: CMMG AR 5.56mm 10.5in Barrel Sub-Assm CMMG 55D8D0A: Barrel Sub-Assm 10.5in MT 4140CM Salt Bath Nitride 5.56mm