This Aero Precision 5.56 Complete BCG is one of the highest rated and most popular Bolt Carrier Group BCG. That's because changing out the BCG is one of the easiest AR15 modifications you could make and Aero Precision is synonymous with quality. These Bolt Carrier Groups are constructed from 8620 tool steel (and 9310 steel for the bolt), shot peened, and magnetic particle inspected, so you can trust that they're built to last. The Aero Precision 5.56 Complete BCG features military specifications (mil-spec), including the gas key and extractor spring. Also, in the carrier itself, Aero machined forward assist serrations. It's also available in a variety of high-end finishes like phosphate, nitride, and nickel boron, but no matter the finish, it gets polished, so in the end you have an easier time cleaning dirt and carbon build up. If you plan on modifying your AR rifle, grab the Aero Precision 5.56 Complete Bolt Carrier Group BCG today! Specifications for Aero Precision AR15 5.56mm Bolt Carrier Group: Manufacturer: Aero Precision Cartridge: 5.56x45mm NATO Gun Make: AR Platform Gun Model: AR-15 Condition: New Bolt Material: 9310 Steel Carrier Material: 8620 Steel Features of Aero Precision AR15 5.56mm Bolt Carrier Group BCG M16-cut carrier Machined from 8620 Tool Steel (Carrier) and 9310 Steel (Bolt) Carrier has forward assisted serrations Black Nitride Finish - advanced lower friction coating that minimizes the need for lubricants and cleaning Properly staked gas key Shot peened HPT tested/MPI marked Black o-ring insert on extractor High quality BCG Shrouded firing pin Nickel Boron Coating inside and out (Bolt, Carrier, and Gas Key) Forged Mil-Spec gas key attached with Grade 8 hardware and Properly staked. 5.56 Bolt is shot Peened and MPI Mil-Spec Extractor Spring, black extractor insert, Viton O-Ring Tool Steel Extractor High quality BCG Forged Mil-Spec gas key attached with Grade 8 hardware and Properly staked. 5.56 Bolt is shot Peened and MPI Mil-Spec Extractor Spring, black extractor insert, Viton O-Ring Tool Steel Extractor High quality BCG Package Contents: Aero Precision AR15 5.56mm Bolt Carrier Group