Cryptic AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group Chrome Black Nitride. 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; includes tool steel extractor with spring and viton O-ring; firing pin chromed finished with firing pin retaining pin and cam pin. HPT (High Pressure Batch Tested) and MPI (Magnetic Particle Inspected). Specifications for Cryptic AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group: Manufacturer: Cryptic Finish: Chrome Fabric/Material: 8620 Aircraft Quality Steel Caliber: 6.5mm Creedmoor Gun Make: AR Platform Gun Model: M16 M4 AR-15 Weight: 17.8 oz Package Contents: Cryptic AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group What firearm models does the manufacturer say Cryptic AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group is compatible with? The manufacturer suggests that Cryptic AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group is compatible with AR-15 M4 M16Cryptic CC-0306: AR15/M16/M4 6.5mm Creedmoor Bolt Carrier Group Chrome Black Nitride