Aero Precision APRH100019C: The heart of every AR-15 is the bolt carrier group. It is one part you do not want to skimp out on. You need to be able to trust it to handle an insane amount of pressure. That is why these Aero BCG\'s are so popular, they are overbuilt and extremely well made. Grab one for your new build or an existing rifle you will not be disappointed. Features: M16-cut carrier Machined from 8620 steel Carrier has forward assist serrations Mil-Spec phosphate coating Properly staked gas key Chrome lined gas key and bolt channel 5.56 Bolt is machined from Carpenter 158 tool steel Shot peened HPT tested/MPI marked Black o-ring insert on the extractor High-quality BCG