Cryptic .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group BCG Left Hand Dragon's Breath. Coated bolt carrier group (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; 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 .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group (BCG): Manufacturer: Cryptic Color: Dragon's Breath Caliber: 5.56x45mm NATO .300 AAC Blackout .223 Remington Gun Make: AR Platform Gun Model: M16 M4 AR-15 Weight: 11.55 oz Features of Cryptic .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group (BCG) Coefficient of Friction 0.2 Hardness 3200 Vickers Max Temperature 750? F Thickness 2-3 microns Reduced Carbon Fouling Easier Cleaning Package Contents: Cryptic .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group What firearm models does the manufacturer say Cryptic .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group (BCG) is compatible with? The manufacturer says that Cryptic .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group (BCG) is compatible with AR-15 M4 M16Cryptic CC-0110-LH: .223 / 5.56 / .300 AAC Blackout Bolt Carrier Group Left Hand Dragon's Breath