The BCM (MPI) complete bolt carrier group is a high-performance component for AR-15, M16 or M4 firearms. Features a fully-assembled auto-version bolt carrier group with a Parkerized exterior and chrome-lined interior for durability and smooth operation. Precision machined to USGI specifications, the M16/M4 carrier includes a mil-spec gas key that is chrome-lined and heat treated to GI standards. The gas key is securely attached with USGI domestic manufacturing grade 8 fasteners and properly staked to meet mil-spec requirements, ensuring reliable gas system function. Constructed from mil-spec Carpenter No. 158 steel, the bolt assembly is known for its strength and resilience, with shot peening for enhanced durability. Includes a tool steel machined extractor and ejector, along with a BCM Extractor Spring for consistent and reliable performance. Undergoes rigorous HPT (High pressure testing) and MPI (magnetic particle Inspection) to verify integrity and functionality. Each BCM bolt carrier group is test-fired before leaving the factory to ensure flawless operation, with handling marks indicative of stringent quality control processes. The BCM complete bolt carrier group is a superior choice for those seeking reliability and precision in firearm components.