Coated Bolt Carrier Group BCG (full auto version) for AR15, M16, or M4 machined from Mil-Spec 8620 aircraft quality steel with shrouded firing pin and Mil-Spec chrome lined interior. BCG includes the proper chrome lined and heat treated gas key. Gas key is secured to carrier with Grade 8 fasteners and properly staked per Mil-Specs. This ensures a strong staking and proper gas system functioning. The bolt assembly is CNC machined from Mil-Spec Carpenter No. 158 steel and shot peened for increased strength per Mil-Spec. HPT (High Pressure Batch Tested) and MPI (Magnetic Particle Inspected). Specifications for Cryptic 6.5mm Grendel/7.62x39mm Bolt Carrier Group (BCG) - Complete: Manufacturer: Cryptic Fabric/Material: 8620 Aircraft Quality Steel, Carpenter 158 Steel Caliber: 6.5mm Grendel, 7.62x39mm Gun Make: AR Platform Gun Model: M16, M4, AR-15 Hand: Ambidextrous Included Accessories: Standard Condition: New Weight: 11.55 oz Bolt Material: Steel Carrier Material: 8620 Steel Features of Cryptic 6.5mm Grendel/7.62x39mm Bolt Carrier Group BCG - Complete Reduced Carbon Fouling; Easier Cleaning; Full Auto Carrier (Backward compatible with all semi-auto rifles) Package Contents: Cryptic 6.5mm Grendel/7.62x39mm Bolt Carrier Group - Complete Gas Key Key Staked with Grade 8 Screws Bolt w/ Spring and Ejector Extractor w/ Spring and viton O-ring Firing Pin Cam Pin