Colt 9mm BCG.
Same BCG that's used in the Colt Submachine Gun (SMG), ready for installation in your 9mm AR-15 conversion. Fits into Colt-pattern upper receivers, and functions with Colt SMG-compatible magazines, including those from Brownells, Metalform, and Pro-Mag. Carrier has correct-length shroud on the underside to trip the auto sear on full auto ARs. Modified 9mm blowback carrier key is staked so it won't work loose, and it's fully compatible with standard AR15/M16 charging handles. Carrier requires the use of a 9mm-specific hammer. Comes fully assembled with all sub-components installed, including firing pin/spring/retaining pin, extractor, and extractor spring.