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. It's what drives the entire gun. If you look at the AR platform's cycle of operations, everything happens around the bolt carrier group. Locking, unlocking, extracting, ejecting, all of it begins with the bolt carrier group. FeaturesBolt:Precision machined from Carpenter Technology No. 158 chrome-nickel alloyHeat treated per mil-spec,Shot peened per ASTM B851/SAE AMS2430S,Vibratory tumbledIndividual high pressure/proof (HP) testFull Auto test fired at assemblyIndividual magnetic particle inspection ASTM E1444/E1444M (MP)Markings deep laser engraved (SP=Shot Peened, HP=High Pressure Tested, MP=Magnetic Particle Inspection.)Extractor:Precision machined from 4340 tool steel alloy per SAE AMS6415T/AMS6484D (vs 4140)Heat treatedShot peen per ASTM B851/SAE AMS2430SExtractor Retaining Pin:Precision machined and ground S7 Tool...