First, it probably doesn’t really matter and I probably wouldn’t suggest throwing it out or buying another one (what I personally would do is probably different than what I’d suggest for someone else)
Now for minutiae...
Maybe a decade ago I started working on a far more detailed write up to go with The Chart. I got really into the weeds regarding the various ratios of various steels, why one recipe did one thing vs another, etc. I can’t even seem to find that research today.
However, my take is this...
Assuming that 9310 was available when the AR system was designed, I only see two possibilities
1) c158 is better for the system, as designed
2) the original designer(s) got it wrong
I prefer to trust in the designers, and go with the material they chose. When it comes to the internals of the gun, my preference is to start with the as-designed system and only deviate when there is a proven good improvement, and even then, what exactly is the impact of that improvement and does that improvement relate to me (a car with better gas mileage is “better” economically, but if I have a company gas card, what do I care?)
There is that other possibility. That 9310 wasn’t available when the gun was designed. But that still doesn’t mean it’s better, just different.
And no matter what, you have to ask yourself why a manufacturer would choose 9310, and for that we can also look to which manufacturers use 9310. Did they choose it because it’s “better”, or because it’s cheaper, more readily available and easier to source (which is also effectively “cheaper” for a business), or, like the bushmaster giant gas ports that were designed to make the guns run with almost any cheap ammo in order to reduce warranty returns, is there some benefit to the manufacturer that isn’t even clear?
I've got a metallurgy guy...hopefully @kedminster will weigh in sooner or later.
#RESIST
Karl Edminster
Energetic Armament LLC
https://energeticarms.com/
Springfield Armory uses 9310 to craft the BCG included with the SAINT rifles, if that is any indication. They do at least pin the gas block and stake the gas key and castle nut.
Has anyone had the actual bolt carrier break (crack, etc)? Not talking about the bolt, or the key, but the carrier itself? what metal are the carriers made from?
eta: I just paid $200 for a spare bolt for my SR15. At least KAC makes choosing the parts easy, LOL
"Customer is very particular" -- SIG Sauer
Nothing so needs reforming as other people's habits - Mark Twain
Tact is the knack of making a point without making an enemy / Where is the wisdom we have lost in knowledge?
From what I've read, it's a somewhat similar steel that is suitable for AR 15 bolts but more widely available, and thus cheaper. Carpenter 158 is apparently bought from a sole-source supplier with a close hold on the production rights. It's the "gold standard" for AR15 bolts, but it's expensive because of its trade name, not because it's a wonder steel that is the "best" possible steel in 2020.
*I am not an engineer, just passing on what I've read from engineers.
"Are you ready? Okay. Let's roll."- Last words of Todd Beamer