Cryptic AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group Mystic Gold. 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 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group: Manufacturer: Cryptic Finish: Matte Caliber: .22 ARC (Advanced Rifle Cartridge) 6.5mm Grendel II 6mm ARC Gun Make: AR Platform Gun Model: M16 M4 AR-15 Features of Cryptic AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group Mil-Spec CNC Machined from 8620 Tool Steel case hardened to 58 60 rockwell with chrome lined interior Mil- Spec Chrome Lined Gas Key Key Staked with Grade 8 Screws per Mil-Spec Mil-Spec Carpenter 158 Bolt Mil-Spec Ejector w/ Spring Mil-Spec Extractor w/ Wolff Spring viton O-ring and insert Mil-Spec Firing Pin w/ Chrome Finish Mil-Spec Cam Pin Package Contents: Cryptic AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group What firearm models does the manufacturer say Cryptic AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group is compatible with? The manufacturer suggests that Cryptic AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group is compatible with AR-15 M4 M16Cryptic CC-LMS-1201: AR15/M16/M4 6.5 Grendel Type II/6mm ARC/22ARC Low Mass Steel Bolt Carrier Group Mystic Gold