These 5.56 / 300 BLK Bolt Carrier Groups are Phosphate Coated with Chrome Lined Gas Key & Bolt Channel, Full-Auto rated, properly staked, and the bolts are Matched to the barrel. Our Rosco Phosphate Bolt Carrier Groups are designed to meet the modern-day carbine shooters requirements.For our Phosphate Bolt Carrier Groups - we choose to team up with the best - Microbest , so the end user has dependability time after time, every time.We have also balanced input from our consumers and military end users in order to bring you the product you need, not just the one we want to sell you.These BCG's are to MIL Specification and have a properly staked gas key along with a chrome lined coating for extended performance. They also feature a Shot Peened/ MP tested Matched bolt (with upgraded extractor) which is designed to lock up perfectly with our extensions for extreme accuracy. These BCG's are made to withstand Full-Auto rated fire and unforgiving use from the end user.Carrier Material: 8620 SteelGas Key: 4130 Steel, attached with Grade 8 hardware, properly stakedCam Pin: Hardened 4340 SteelFiring Pin: 8740 Steel, Heat Treated, Mil-Spec, Center-less ground, Hard Chrome PlatedBolt Material: C158, , Phosphate Coated, MPI/HPTExtractor: 4140 Steel, Heat Treated, Shot PeenedEjector: S2-S7 Tool Steel, Shot PeenedOur Phosphate/Chrome BCGs ship with upgraded Sprinco Extractor Kit