Franklin Armory 5.56 NATO Bolt Carrier Group BCG Black. 56 NATO. 6.8 SPC. 6.5 Grendel. 7.62x39. 450 BM. Carrier machined from 8620 Steel. M16 Weight. Properly staked gas key. Polished finish. Franklin Armory logo included. Treated with Salt Bath Nitride or Nickel Boron. Bolt Machined from 9310 or 158 Carpenter steel (depending on availability). Includes Extractor O-Ring. Stainless Steel Firing Pin. Specifications for Franklin Armory AR-15 Bolt Carrier Group (BCG): Manufacturer: Franklin Armory Finish: Polished Fabric/Material: 9310 Steel 8620 Alloy Steel Stainless Steel Carrier Material: 8620 Steel Bolt Material: 9310 Steel Caliber: 5.56x45mm NATO Gun Model: AR-15 Included Accessories: Extractor O-Ring Gas Key Carrier Bolt Firing Pin Package Contents: Franklin Armory AR-15 Bolt Carrier Group What firearm models does the manufacturer say Franklin Armory AR-15 Bolt Carrier Group (BCG) is compatible with? The manufacturer says that Franklin Armory AR-15 Bolt Carrier Group (BCG) is compatible with AR-15Franklin Armory 00-52018-BLK: 5.56 NATO Bolt Carrier Group Black