LMT Bolt Carrier Group (MPI) - Semi-Auto (Price $120.00) Bolt carrier group (Semi-auto version) for your AR15, M16, or M4.  Parkerized exterior and chrome lined inside carrier. Machined to USGI specifications.  This M16/M4 carrier includes the proper Mil-Spec gas key.  Gas key is chrome lined and heat treated per GI specifications.  Gas key is secured to carrier via USGI domestic mfg Grade 8 fasteners and properly staked per Mil-Specs.  These properly hardened parts insure a strong staking and proper gas system functioning. The bolt assembly is machined and steel, shot peened for increased strength, includes tool steel machined extractor and ejector, BCM™ Extractor Spring, and is MPI (Magnetic Partical Inspected).