I think you may be overestimating the number of actual engineers in any but the biggest AR makers.
But yes, I’ll concede it’s a general rule based on my lack of trust and understanding of the AR market, rather than an absolute impossibility.
According to H&M Metal Processing They have developed a proprietary process using lower temperature and exposure time that achieves the benefits of SBN while maintaining core hardness.
prepare, thank you for looking into this and reporting back.
Assuming what H&M says is true, now the trick is to find out which bolts have been nitrided by them using this process. My understanding (which could be wrong) is that there are not a lot of companies that do large scale nitriding on firearms parts in the U.S.
Joe Mamma
I hope to get some additional information I requested from H&M.
Currently I’m only certain of 2 manufactures that have their BCG’s nitrided at H&M. Not sure if any Tier one manufactures use them or not?
exactly…
Anyone have bolt lug wearing or shearing with their 9310. Seems it’s more common than on a C158 bolt.
What sort documentation or proof do you have that makes this statement a fact, instead of an opinion ?
9310 can / should be better than C-158, but it all depends on who does the heat treatment.
AR bolts do fail, you should carry a spare.
Phosphate 9310 bolts exist.
Steels are a funny material, you gain something, you give something up. Increased hardness can lead to a brittle steel if not properly heat treated. Also, a shitty C-158 heat treat will be just as disastrous as a shitty 9310 heat treat.
I’ll remind everyone the TDP was written a long long time ago and there has been SIGNIFICANT advancement in metallurgy since that time.
You need look no further than what is happening in the knife world to realize there are probably other viable options that exceed the performance of C-158 for use in bolts.
Be open minded to change and learn about the better options that are very likely out there.
Unfortunately, that hasn’t always translated into better spring life. Early LMT bolts suffered extraction problems. I have an early LMT E bolt and had extraction problems from the start due to weak extractor springs. I fixed the problem by counting the coils of the original springs and cutting down springs of the same diameter to the same count. With the same coil count, the replacement springs were longer and applied greater force to the extractor.
The springs I used were from an LPK, detent springs or something (I don’t remember exactly which spring). So far, the extraction issues haven’t returned.
As far as print changes go- How much it costs to change a print depends on what’s being changed. Changes to prints are expected and routine. It shouldn’t cost a half mil to update a print change letter and add a line to the materials list, especially one as simple as for manufacturing an AR bolt. A change to the body of the print wouldn’t be necessary.
I have heard that 9310 is supposed to be a lot stronger and a much better performing bolt. I have heard that 9310 can last upwards of 10k rounds were as 158 is 3-5k. That being said I have a 158 that has somewhere around 8-9k and its still fine. Actually all my 158 bolts are still rocking and over 3k for each at least. I love constant improvement and I am guilty of every new improvement to a system automatically means that the previous one is shit now. I feel and have seen multiple testings done that do show 158 lugs shearing well before 9310, just never had it happen in my life. I think if you are shooting a lot of 855 A1 or other very high pressure rounds then there may be a difference, but I think at the rates that civilians shoot, I see it as negligible.
I would suspect that many aren’t opposed to a better material for a bolt like 9310. The concern I have is whether or not there will be a standard to which a 9310 bolt will be manufactured to meet, and will that standard be followed? Milspec doesn’t always mean the best, but it is a spec.
GI bolts typically go somewhere around 12,000-15,000 in rifles shooting standard match ammunition.
3-5K out of a GI bolt would lead me to believe Uncle Sam specs and buys bad bolts, and that’s typically not true.
This is an oft-cited West Point Engineering Study of M16 Bolt Failure (available as a .pdf). It shows sample bolts had some corrosion pitting and material stress from a proper Carpenter 158 bolt that may not have been correctly case-hardened. I don’t think they could say because they didn’t repeat the test with a second lot of properly checked and inspected bolts, limiting the test scope (which would have also allowed repeatable peer-review using scientific method):
Failure Analysis of the M16 Rifle Bolt
V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach
Department of Civil and Mechanical Engineering
United States Military Academy
West Point, NY 10996, USA
“Tramp elements” (impurities?) in 9310 are also a factor. Not all bolts will be the same in that regard. The “wider spread of service life” that Bill Alexander mentions is noteworthy.
It is not necessarily just adding a new, or altered material line, it is all of the required proof and certification that the “new, alternate material” is as good or better than the existing material.
And since the design is technically owned by Colt, they would be the ones responsible to carry out the testing and certification (with funding from the Army). Colt has no real incentive to make major changes to the material as long as they can get Carpenter 158. They wouldn’t make any money off a testing contract, so they can just price the contract beyond what the Army wants to pay. I’ve seen companies do this before.
And curiously, when you look at Carpenters list of elements that make up Carpenter 158, they list no tramp elements.
Tramp elements are elements that are not “specified” in the alloy grade, but an acceptable amount (trace) can be present without any detrimental effect on the alloy’s performance. In most steel you will find phosphorus and sulfur as tramp elements. They generally are left over from the ore or coke and you cannot get rid of them completely. Yet Carpenter 158 does not list them, as they are not “specified” for the alloy. But, you can bet they are there. 9310’s specification lists these tramps as there is a need to keep the amount in check. Carpenter 158, being a proprietary alloy, keeps these values to itself.
Chances are the amount of P and S in 158 is the same as 9310, 0.025%, because that is the best you can realistically do.
As to the 8620 bolt, no. 9310 is a far better bolt material in general than 8620. Generally, US military small arms designed after 1960-ish use 9310 for the bolt, or whatever they used to lock the breech shut in preference to 8620…
M60
M240
M249
M73
I do not think Bill Alexander was suggesting that 8620 makes acceptable bolts but rather that heat treatment can have a greater magnitude of effect than the inherent difference between these alloys.
Amen and while that is certainly true, the average user/consumer has no damn way to tell if something ADVERTISED as Mil Spec is IN FACT MILSPEC-- especially when we are talking about a type of steel, it’s relative hardness etc…You can look at a part and say, “Gee, it sure looks good, the package SAYS Milspec”…but in reality with most things, you have no idea the truth of that statement. None.
And, that is why the Government has a Government employed civil servant at the bolt manufacturing plant who’s jobs is to watch them make bolts and can if he wants, pull random parts off the line and run them through the full gamut of inspections.
For the average consumer, we have to just trust the vendor.
So, pick your vendor carefully.
If there’s no contract strictly for that component (i.e. a specific military bolt contract for replacement parts vice complete rifle or carbine) there might not be a government inspector on-site. The acceptance standard then is for the entire weapon.
Say Colt (strictly for academic discussion) subs-out to Continental, Micro-Best, Toolcraft, or John Doe industries for a component (a complete bolt carrier group for instance) for a rifle contract. If the BCG fails, the government (not factory) inspectors go to the next step in the rifle or carbine spec testing procedure. If that sample fails (say 10 out of a hundred) then a whole batch has to be tested (just for giggles, let’s say 1,000 to 5,000 as I’m too lazy to go back to MIL-DTL-70599C_AMENDMENT-1). If the next-sized batch fails, all weapons are rejected / thrown out. Everything besides the serial-numbered NFA lower can be sold as a commercial weapon, and Colt would have to bring in another batch.
Keep failing batches and federal and defense acquisition regulations may require a formal “Show cause” response to answer why the government shouldn’t penalize you or cancel the contract.
What we’re really saying is that certification of the new material isn’t worth the gain from changing to the new material. The certification process has nothing has nothing to do with the cost of changing the print.
For example, changing the orientation of a fastener on a print (which is a bigger change than updating the material a part is made from) to stop the fastener from causing damage doesn’t cost a half million dollars.