9310 Bolt Data

[sinister]

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.

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

[Disciple]

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?

"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.

The illustration serves that there is considerably more involved in the production of a bolt than simply the selection of what is on paper an adequate material. A metallurgist will select a material from the perceived application. That application must be correctly conveyed by the customer, but ultimately the customer has to determine the material best suited. AISI 9310 has a number of drawbacks in use for the bolt of an M16 type rifle , not least of which is that in this application the fatigue life is lower than Carpenter 158 as a result of certain tramp elements commonly found in the alloy. This is not to imply that Carpenter 158 is the pinnacle for this application but that AISI 9310 is not optimum either. Both have drawbacks and advantages.

The rush to produce AISI 9310 bolts without an understanding of the problems will create not stronger bolts but those with a wider spread of service life.

A well executed 8620 bolt will outperform a higher alloy if it is not well made and heat treated.

Bill Alexander

Referring to 6.5 Grendel bolts:

It goes without saying that the bolts have a good metallurgy and that the heat treatment is improved. The perception is that the alloy is AISI 9310 steel. It is in fact very closely aligned to this but we select an alloy known for its enhanced fatigue life over regular 9310. It is not specifically a stronger alloy just resists crack formation better.

[lysander]

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.

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.

"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.

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

[Disciple]

As to the 8620 bolt, no. 9310 is a far better bolt material in general than 8620.

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.

[Esq.]

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.

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.

[lysander]

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.

[sinister]

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.

[MistWolf]

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.

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.

[sinister]

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 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.

It depends. It could.

I was REALLY surprised the government allowed Beretta to change M9 materials for small components from steel to plastic (safety levers, recoil spring guide rod, I think the trigger, some others).

The change from brown to black hardware finish on the SIG M17/M18 (barrel lock switch, slide catch, and safety levers) was very early in the contract.

Conversely, going from M4 Carbine standard buffer to H took a number of years. I don't know how long it took Colt to go from original CAR/M4 stock to waffle-style, and it took a really long time to go from M4-pattern to SOCOM-pattern barrel -- and it's still not an "M4A2."

The M4A1 the Army buys is still what it provides to USASOC -- but the commandos modify everything else on the gun (including the trigger) with SOPMOD ("Special Operations - Peculiar Modifications").

[MistWolf]

I've worked on projects where we needed to go through aircraft prints and assembly orders with a fine tooth comb to find mistakes so the engineers and planning could make changes. Getting small changes made to the print doesn't cost a lot.

Testing a material for certification or disqualification can cost a lot but it's separate from the cost of changing a print.

Tests for certs can be run all day long on various materials and it doesn't change the cost of a blueprint. The flip side is, blueprints can be changed to have parts made from different materials without prior testing. The monies come from separate budgets.

Colt could call up the Army and say "We want to change the material we make bolts out of."

The Army could say "We want the material tested and certified first and Colt has to pay for." Or they could say "We'll pay for the cert." Or, they could say "9310 has a good track record. Let's do it." While the cost of each certification process may vary, the cost for the draftsman to add to the Parts Material List "Bolt, P/N AR15BOLT Change C Make From 9130 Steel" remains the same.