9310 Bolt Data

[Mysteryman]

TL;DR:

- Milspec isn't the end-all, be-all...it's a benchmark or a minimum standard...NOT the peak of performance
- Bolt life performance depends on how well the rest of the gun is built; a mediocre bolt will last in a well-built gun longer than a better-than-milspec bolt in a poorly built/gassed/timed gun
- Apples-to-apples comparisons are rare but what is probably true is that well-built and properly tested 9310 bolts are just fine.
- Superior alloys materials exist well beyond "milspec". Remember the crash test/recall scene from "Fight Club"...or consider the LMT or KAC "enhanced" bolts. Would you rather a "good" bolt that's gonna cost you $65-75 per bolt or a "great" bolt for $180-250 per bolt?

You're right, but MILSPEC is a specification and even at the minimum, it still meets the standard. The other wonder steels used and special bolts are merely marketing without the thorough and expensive testing mentioned above. MILSPEC bolts have a 60 year track record, 9310 and the other enhanced bolts do not.

[lysander]

You're right, but MILSPEC is a specification and even at the minimum, it still meets the standard. The other wonder steels used and special bolts are merely marketing without the thorough and expensive testing mentioned above. MILSPEC bolts have a 60 year track record, 9310 and the other enhanced bolts do not.

In engineering, you have what is known as "suitability by similarity". If two objects, or materials, are similar enough, you can assess the suitability by examining the similarities and differences (if any). Carpenter 158 and 9310 are very similar steels and in other applications show similar behavior. Further, 9310 does have a long and successful history as a bolt material. I would have to say that 9310 is a perfectly adequate substitute material.

[AAMP84]

You're right, but MILSPEC is a specification and even at the minimum, it still meets the standard. The other wonder steels used and special bolts are merely marketing without the thorough and expensive testing mentioned above. MILSPEC bolts have a 60 year track record, 9310 and the other enhanced bolts do not.

Isn’t the expensive price of the LMT Enhanced bolt partly because of the research and development costs?

[Failure2Stop]

In engineering, you have what is known as "suitability by similarity". If two objects, or materials, are similar enough, you can assess the suitability by examining the similarities and differences (if any). Carpenter 158 and 9310 are very similar steels and in other applications show similar behavior. Further, 9310 does have a long and successful history as a bolt material. I would have to say that 9310 is a perfectly adequate substitute material.

Agreed.

[Mysteryman]

In engineering, you have what is known as "suitability by similarity". If two objects, or materials, are similar enough, you can assess the suitability by examining the similarities and differences (if any). Carpenter 158 and 9310 are very similar steels and in other applications show similar behavior. Further, 9310 does have a long and successful history as a bolt material. I would have to say that 9310 is a perfectly adequate substitute material.

I don't disagree. The reality here is that in the AR platform 9310 has near zero track record compared to carpenter 158. The minute differences between the two isn't enough to make the change to 9310 any significant advantage if any at all. The hype around 9310 is just that.

[prepare]

I don't disagree. The reality here is that in the AR platform 9310 has near zero track record compared to carpenter 158. The minute differences between the two isn't enough to make the change to 9310 any significant advantage if any at all. The hype around 9310 is just that.

The hype stems from the amount of circulated misinformation. Even from industry insiders and so called industry "professionals".

[VIP3R 237]

The biggest issues I’ve seen with 9310 is the result of improper heat treat, and 9310 is much less forgiving with the treatment temperature range. 9310 is harder than C158 but it’s also more brittle, it’s fatigue life is also notably shorter than C158.

SOLGW is also not fond of 9310. https://www.arbuildjunkie.com/ar-bol...mike-mihalski/

Here’s what Bill Alexander stated about 9310

Bolts are becoming a pet subject!

It is always interesting to consider the bolt within the context of its application. To do so will draw not only on stress analysis, but also on fatigue theory and metalurgy. This will quickly move the solution beyond the simple question of which steel is best, for the best steel if applied out of context will not perform adequately.

So for simple illustration let us assume that the steels are applied well, before discussing the differences.

Carpenter 158 is without doubt an excellent material for the production of M16 bolts. The material is clean with negliable elements in the make up that are detrimental to the fatigue life. It can operate happily within the confines of the enviromental requirements imposed by the application and has a very low deformation of the parts as they run through heat treatment. The down side to the material is that it was designed to heat treat in large sections so the thin bolt material will respond somewhat voilently. Again not an immediate problem if the heat treatment is absolutely perfect but within the confines of a production enviroment it will throw problems.

By comparison AISI 9310 will on first inspection also make an adequate bolt material. It has several alloy elements that promote a better structure and in the correct heat treatment will provide a slightly higher toughness than Carpenter 158 which is benificial to the fatigue life. Corrosion resistance is slightly higher but as with C158 it should not be applied without some form of surface protection. Thin section response to quenching is somewaht less than C158 which makes it better suited to the manufacture of bolts. However by comparison to Carpenter 158, AISI 9310 has several elements present in its composition that are detrimental to fatigue while not being evident in the physical properties.

It has become evident from the industry that a number of manufacturers have jumped upon the AISI 9310 wagon in order to claim better performance. While in theory an AISI 9310 bolt may perform better I would not typically select this material specification. There are a wide number of superior alloys available without resorting to the nickel based maraging alloys which are expensive, difficult to machine and extremely temperamental in behaviour. The steel industry has advanced since the specification of Carpenter 158 but the basic premises for the selection remain even if the menu has now expanded.

Bill Alexander

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

[VIP3R 237]

Absolutely this. I work for a AS9100D manufacturer, and project managers and engineers don’t care if there’s better substitutes, they care about what material is certified.

As to the question of why Carpenter 158 was chosen as the material for the bolt, rather that an AISI standard steel alloy (like 9310), here is something I was once told by an engineer at one of the big aerospace component companies. Manufacturers, especially those in the aviation field prefer to use proprietary standards, rather than institutional or Federal standards if they can. Proprietary standards, for something like an alloy composition, are owned by the company and usually trademarked, thus changing the composition is highly unlikely. Further, with a single source, they have some leverage to keep the composition from changing - "I'll only be buying from you as long as you don't change the product."

Institutes, associations and other such organizations, like the American Iron and Steel Institute, do not manufacture anything and, theoretically, can change their specifications on a whim if they see fit. This could mean that the 9310 bought today is not the same as the 9310 bought next year.

Manufacturers fear not have tight control of their material supply. While this is a logical concern, especially in the aerospace industry, it is really not something I have ever heard of; a specification changing so drastically that it is unfit for applications that previously used it, but that seems to be the way some companies think.

[prepare]

The biggest issues I’ve seen with 9310 is the result of improper heat treat, and 9310 is much less forgiving with the treatment temperature range. 9310 is harder than C158 but it’s also more brittle, it’s fatigue life is also notably shorter than C158.

SOLGW is also not fond of 9310. https://www.arbuildjunkie.com/ar-bol...mike-mihalski/

Here’s what Bill Alexander stated about 9310

The heat treat issues sited are when 9310 bolts in the AR were initially introduced and they continue to brought up again and again.
Is there any recent data that 9310 bolts are still failing more than C158?

[Biggy]

The Geissele Stressproof Bolt is made from Carpenter 158, however this is not your typical material spec’d by the US Government. Since Geissele wanted to take it to the next level, their engineers worked directly with the Carpenter Steel metallurgists in Reading PA, to produce a special heat of material known as **Carpenter 158+**. This material is cleaner with less impurities, ultimately making it stronger and more consistent. They did not stop there, they decided to forge the bolt. Using the same process used to produce upper and lower receivers, a forged bolt manipulates the grain structure of the metal and yields a bolt capable of 5 times the life of a mil-spec bolt. Each bolt is then rigorously inspected, high pressure tested, mag particle inspected and coated with Nanoweapon for maximum corrosion and wear resistance.

Nanoweapon is a family of coatings similar to DSL (Durable Solid Lubricant) that was developed by Picatinny Arsenal (US ARMY ARDEC), and is only available exclusively from Geissele Automatics. Their engineers worked for over 3 years with the research and development company that worked with Picatinny to develop the coating in order to fine tune it into what it is today, making it the pinnacle of coatings for firearm components. No other coating on the market can provide the same level of corrosion, wear, and abrasion resistance as Nanoweapon. The coating is applied at low temperatures so it does not affect the metallurgy of the part, and has a surface hardness equivalent of 82HRC. At that hardness, it is harder than sand, easily rejecting carbon and making cleaning a breeze, on top of allowing the firearm to operate normally with less lubrication.