These 5.56/300 BLK Bolt Carrier Groups are phosphate-coated with chrome-lined gas key and bolt channel, full-auto rated, properly staked, and the bolts are matched to the barrel. Their Rosco phosphate bolt carrier groups are designed to meet modern carbine shooters’ requirements. For their phosphate bolt carrier groups, they team up with the best-Microbest-so the end user receives dependable performance every time. They have also incorporated feedback from consumers and military end users to deliver the products you need, not just what they want to sell. These BCGs meet MIL specifications, with a properly staked gas key and a chrome-lined coating for extended durability. They feature shot peened, MP-tested matched bolts with upgraded extractors, designed to lock perfectly with their extensions for extreme accuracy. Built to withstand full-auto firing and tough use from the end user.