M2 Armament Group AR-15 5.56/.223/.300 Nitride Bolt Carrier Group Black. Purpose-built for demanding law enforcement armorers competition shooters and custom rifle builders this full-auto profile M16 BCG delivers smooth cycling maximum lubricity and uncompromising strength across 5.56x45mm NATO .223 Remington .300 AAC Blackout and .350 Legend rifle builds. Specifications for M2 Armament Group AR-15 5.56/.223/.300 Nitride Bolt Carrier Group: Manufacturer: M2 Armament Group Color: Black Finish: Nitride Carrier Material: 8620 Steel Caliber: 5.56x45mm NATO .300 AAC Blackout .223 Remington Gun Make: AR Platform Gun Model: AR-15 Full Auto Rated: Yes Package Contents: M2 Armament Group AR-15 5.56/.223/.300 Nitride Bolt Carrier Group What firearm models does the manufacturer say M2 Armament Group AR-15 5.56/.223/.300 Nitride Bolt Carrier Group is compatible with? The manufacturer says that M2 Armament Group AR-15 5.56/.223/.300 Nitride Bolt Carrier Group is compatible with AR-15M2 Armament Group M2-BCG-556: AR-15 5.56/.223/.300 Nitride Bolt Carrier Group Black