RISE Armament's .308 advanced bolt-carrier group (BCG) is manufactured with precision and individually inspected to ensure high-level performance - Key Features - High-strength and easy-to-clean black nitride finish - Individually MPI tested - Bolt: 9310 MPI tested - Carrier: 8620 tool steel heat treated and case hardened - Gas key: tool steel - grade 8 hardened fasteners and staked properly - Cam pin: 4140 steel - Extractor: tool steel