Cryptic Low Mass Bolt Carrier Group BCG - Complete .223/5.56/.300 AAC Blackout Mystic Gold. Carrier is machined from Mil-Spec 8620 tool steel with shrouded firing pin and Mil-Spec chrome lined interior. BCG includes the Mil-Spec chrome lined and heat treated gas key. Gas key is sealed then secured to carrier with Grade 8 fasteners and properly staked per Mil-Specs. This ensures proper gas system functioning. The bolt assembly is CNC machined from Mil-Spec Carpenter No. 158 steel then shot peened for increased strength per Mil-Spec. HPT (High Pressure Batch Tested) and MPI (Magnetic Particle Inspected). Specifications for Cryptic .223/5.56/.300 AAC Blackout Low Mass Bolt Carrier Group (BCG) - Complete: Manufacturer: Cryptic Finish: Chrome Plated Fabric/Material: 8620 Aircraft Quality Steel Carpenter 158 Steel Carrier Material: 8620 Steel Bolt Material: Steel Caliber: 5.56x45mm NATO .300 AAC Blackout .223 Remington Gun Make: AR Platform Gun Model: M4 M16 AR-15 Hand: Ambidextrous Weight: 8.2 oz Condition: New Additional Features: Thickness - 2-3 microns Included Accessories: Standard Features of Cryptic .223/5.56/.300 AAC Blackout Low Mass Bolt Carrier Group BCG - Complete Reduced Carbon Fouling; Easier Cleaning Package Contents: Cryptic .223/5.56/.300 AAC Blackout Low Mass Bolt Carrier Group - Complete Gas Key Key Staked with Grade 8 Screws Ejector w/ Spring Extractor w/ Wolff Spring viton O-ring and insert Firing Pin Cam Pin What firearm models does the manufacturer say Cryptic .223/5.56/.300 AAC Blackout Low Mass Bolt Carrier Group (BCG) - Complete is compatible with? The manufacturer says that Cryptic .223/5.56/.300 AAC Blackout Low Mass Bolt Carrier Group (BCG) - Complete is compatible with AR-15 M4 M16Cryptic CC-LMS-0101: Low Mass Bolt Carrier Group - Complete .223/5.56/.300 AAC Blackout Mystic Gold