BCG discussion

[Nephrology]

Going through my box o’ stuff this afternoon I found one of these bolts I’d forgotten I’d picked up a while back.

According to the specs it’s 9310 instead of 158. I’m not a metallurgist so I don’t know the significant differences between the two. I’ll keep it as a spare but if I’m not running full auto, does it make a tinker’s damn that it’s not 158??

afaik there is a lot of handwringing about this but i have no reason to believe 9310 steel bolts are meaningfully different from c158 bolts. I did a lot of googling on this, and found a lot of long debates on M4C but nothing really definitive.

[rob_s]

Going through my box o’ stuff this afternoon I found one of these bolts I’d forgotten I’d picked up a while back.

According to the specs it’s 9310 instead of 158. I’m not a metallurgist so I don’t know the significant differences between the two. I’ll keep it as a spare but if I’m not running full auto, does it make a tinker’s damn that it’s not 158??

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?

[LittleLebowski]

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.

[kedminster]

I've got a metallurgy guy...hopefully @kedminster will weigh in sooner or later.

Unfortunately I am not familiar with either of these alloys and neither is listed in the most recent MMPDS. I would agree that alloy is just one factor and heat treat and surface finish may be just important, if not more important, than the base alloy itself.

[tlong17]

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.

[theJanitor]

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

[SecondsCount]

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

I was going to ask the same thing. I haven't seen a bolt or bolt carrier break in years, and the last time was on a carbine upper that a friend had who was bragging that he paid $250 for the complete setup.

[ReverendMeat]

https://faxonfirearms.com/blog/why-9...ar15-m16-bolt/

[awp_101]

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?

All fair and valid questions.

I think 9310 is a "recent" alloy, or at least newer than the original milspec for the AR. Is it possible it's an alloy that provides the attributes of 158 (or close enough) while being easier on tooling?

[TGS]

All fair and valid questions.

I think 9310 is a "recent" alloy, or at least newer than the original milspec for the AR. Is it possible it's an alloy that provides the attributes of 158 (or close enough) while being easier on tooling?

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.