CMMG Barrel and BCG Kit 8in 4140CM SBN 10MM. Unlike typical direct blowback systems our RDB uses a bolt that is forced to rotate slowing the BCG. This results in a lighter BCG for a lighter rifle and less felt recoil than a straight blowback system. Specifications for CMMG 10mm Barrel And Bcg Kit: Manufacturer: CMMG Color: Black Finish: No Fabric/Material: 4140CM Caliber: 10mm Auto Barrel Length: 8 in Barrel Profile: Medium Taper Threads per Inch: .578x28 Barrel Twist Rate: 1-16 Flutes: No Weight: 2.1 lb Condition: New Package Contents: CMMG 10mm Barrel And Bcg Kit CMMG 10D424E: Barrel and BCG Kit 8in 4140CM SBN 10MM