Cryptic 6.5 Grendel - Type ll Bolt Carrier Group BCG 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 6.5 Grendel - Type ll Bolt Carrier Group (BCG): Manufacturer: Cryptic Fabric/Material: 4140 heat treated steel Caliber: 6.5mm Grendel II Gun Make: AR Platform Gun Model: M16 M4 AR-15 Hand: Right Weight: 11.55 oz Condition: New Features of Cryptic 6.5 Grendel - Type ll Bolt Carrier Group (BCG) Mil-Spec BCG Machined from 8620 Aircraft Quality Steel and heat treated to 60-61 RC Mil- Spec Gas Key Key Staked with Grade 8 Screws per Mil-Spec Mil-Spec Carpenter 158 Bolt w/ Spring and Ejector Tool Steel Extractor w/ Spring and viton O-ring Mil-Spec Firing Pin w/ Chrome Finish Mil-Spec Cam Pin Full Auto Carrier (Backward compatible with all semi-auto rifles) BCG Weight 11.55 oz. Package Contents: Cryptic 6.5 Grendel - Type ll Bolt Carrier Group What firearm models does the manufacturer say Cryptic 6.5 Grendel - Type ll Bolt Carrier Group (BCG) is compatible with? The manufacturer suggests that Cryptic 6.5 Grendel - Type ll Bolt Carrier Group (BCG) is compatible with AR-15 M4 M16Cryptic CC-1206: 6.5 Grendel - Type ll Bolt Carrier Group Black Nitride