Aero Precision APRH100070 AR-15 Bolt Carrier 223 Remington/5.56 NATO This Nickel Boron bolt carrier is an eye catching addition to your AR build. It features Mil-spec dimensions and coating, is made of steel, with a shrouded firing pin, Mil-Spec extractor spring, black extractor insert, Viton O-ring, and a tool steel extractor.