The Dirty Bird Enhanced Bolt Carrier Group for .223/5.56 features a unique full-auto carrier design with practical improvements in two key areas: Strategically relocated load bearing surfaces reduce carrier tilt/can't during recoil, thus increasing reliability and longevity. Additional wall thickness in the gas exhaust port area for added strength and rigidity.The 9310 Bolt is machined to mil-spec dimensions and then the external surfaces including the lugs are CNC ground after the heat treating process to ensure a very precise fit. The bolts themselves feature the same Black Nitride finish as the carrier and are High Pressure (HP) Tested and Magnetic Partical Inspected (MPI) in accordance with Mil-STD-1816 specifications.