This is a standard bolt manufactured by Lewis Machine & Tool and is one of the best standard bolts available on the market. Given the quality of these bolts, they are a great reliability upgrade for weapons which didn't come with top tier bolts, or are in need of replacement after more than 5000 rounds.
This bolt is one of the few bolts available to civilians that is manufactured to mil-spec requirements and it is both high pressure test (HPT) fired and magnetic particle inspected (MPI). This extensive testing is why all LMT bolts come with brass marks and firing residue.
These are one of the very few sources for top tier MILSPEC bolts, buy with confidence!