9310 is a far more widely used material in the metal industry than is C-158, & IF, & that's a REALLY big IF, it's heat treated correctly, it may be marginally better for an AR bolt than C-158..................but it is not mil-spec for a bolt, only C-158 is.
The issue is that since 9310 is much more readily available, basically a commodity, and not all of it is HT'd by the same HT'er with the same competency levels, there's much more variability in the stock than there is in the relatively lower volume, smaller supply based, C-158, which is more tightly controlled, but also more expensive.
And that is the reason to only buy bolts from proven & known reliable suppliers...............because they are only buying stock (or bolts) from known consistent & high quality steel suppliers.
Why do you think that companies like Anderson, Radical Firearms & Bear Creek products have a higher incidence of failure than do companies like BCM, Daniel Defense, Toolcraft, Rubber City Armory, etc., do?..................in big part, it's due to the consistency & quality of the steel.
And I ain't gonna buy jack-schitt from a company like Integrity Arms & Survival w/o a really, really good idea of who is making their parts. There's just too many other reliable options.
JMHO, YMMV
MM
MM, you hit on some great points, but some of these guys may not know metallurgical differences between different materials. You are correct about the heat treating and carpenter 158 vs 9310. 158 is mil spec, that is good and generally when manufactures say its c158, you can bet its good. Some say 9310 is better, but most times its heat treated all the way through, and C158 is surface hardened. In some instances surface hardening is better because it offers better impact resistance, where 9310 may be more brittle (depending on how and who heat treated it). Now, keep in mind, we are just talking about the bolt. The carrier is slightly different, as it doesnt need to be made from 9310 to be an excellent bolt carrier group (BCG). 8620 (as in the material used in the carrier i shared earlier) is a great material for use in a carrier. Surf the web or talk to anyone, and youll be hard pressed to find anyone that has ever had an 8620 carrier fail. Now, going back to bolts (The actual bolt itself), 8620 is less than mil spec rated and there have been failures associated with using it for the bolt itself. C158 is the only way to fly there. A while back PSA put out a run of 8620 bolts. Guys should check to make sure what they have in their ars. If you know you have a bolt that is 8620, keep an eye on it. Inspect it good after every cleaning, or just toss it and put a C158 in your carrier. That will add piece of mind and you'll have a far better BCG.
