The CMMG16" 40 S&W MkGs Barrel and BCG Kit allow you to build a Pistol Caliber Carbine using our Patent Pending Radial Delayed Blowback System. Unlike typical direct blowback systems, our RDB uses a bolt that is forced to rotate and unlock, slowing the BCG. This results in a lighter BCG for a lighter rifle, and less felt recoil than a straight blowback system.Our MkGs Barrel and Bolt Kits are designed to work exclusively with our MkGs Lowers. Other manufacturers' receivers may work, but we cannot guarantee function or reliability.All CMMG products come with our Lifetime Quality Guarantee.