6.5 Grendel (Type 2) Wilson Combat Nickel Boron Bolt Carrier Group by Wilson CombatWilson Combat bolt carrier group (full auto version) for your AR15, M16, or M4. Nickel Boron Coated. This M16/M4 carrier includes the proper Mil-Spec gas key. Gas key is chrome lined and heat treated per USGI specifications. Gas key is secured to carrier via USGI domestic mfg Grade 8 fasteners and properly staked per Mil-Specs. These properly hardened parts insure a strong staking and proper gas system functioning.