The Microbest BCG has been designed from the ground up with the most avid shooters in mind, using only the best materials available on the market today. The bolt assembly is machined from Carpenter No. 158® steel, shot-peened, MP marked, HP tested, and has a tool steel extractor that is machined from bar stock. Made in the U.S.A. and covered by a lifetime warranty, you can count on this BCG for a lifetime of service. Features: 4340 Extractor spring, mil-spec insert and extractor retainer pin in mag phosphate Mag phosphate ejector Mil-spec stainless gas rings