Sons of Liberty Gun Works looks at the bolt carrier group as the heart of the gun. If the gas port is the lungs, then the bolt carrier group is the heart. Its what drives the entire gun. If you look at the AR platforms cycle of operations, everything happens around the bolt carrier group. Locking, unlocking, extracting, ejectingall of it begins with the bolt carrier group.Features :Full Auto Rated and ProfiledBolt is precision machined from Carpenter Technology No. 158 chrome-nickel alloy, Carrier is machined from AISI 8620 aircraft quality alloySons of Liberty Battle Flag logo deep laser engravedManganese Phosphate Finish