View Full Version : 9310 Bolt Data
When were 9310 bolts first introduced?
Early on there were some issues with properly heat treating that led to breakage. Has that since been corrected? If so when?
Some say a properly heat treated 9310 is better than mil-spec C-158?
C-158 bolts are available in both phosphate and nitride, it appears all 9310 bolts are nitride only?
Has Crane tested 9310 bolts with the latest heat treatment processes?
Are there any drawbacks to a properly heat treated 9310 bolt?
Are 9310 bolts still considered unproven?
1) When were 9310 bolts first introduced?
2) Early on there were some issues with properly heat treating that led to breakage. Has that since been corrected? If so when?
3) Some say a properly heat treated 9310 is better than mil-spec C-158?
4) C-158 bolts are available in both phosphate and nitride, it appears all 9310 bolts are nitride only?
5) Has Crane tested 9310 bolts with the latest heat treatment processes?
6) Are there any drawbacks to a properly heat treated 9310 bolt?
7) Are 9310 bolts still considered unproven?
1) The first bolt made from 9310 I know of was made sometime around 1964.
2) There were? I never heard of wide spread problems.
3) And, some say the opposite. Everybody has an opinion.
4) This is more of a statement than a question.
5) Why should NSWC Crane want to test bolts?
6) They aren't "MIL-SPEC" for the M16/M4.
7) Bolts made from 9310 have been used on M60s and M249 for many decades without any issue. According to a 1962 report by Watertown Arsenal, 9310 steel was not only more tolerant of heat treating condition variations than the then 'standard' 8620 steel, it was superior in strength. For these reasons the 9300 series steels have been very popular in weapons breech bolts.
Hodge Defense uses a 9310 bolt in their ARs so the concept is proven. Just like any other gun product, if they’re made right they’re good. If they’re not, the forums have more to talk about.
1) The first bolt made from 9310 I know of was made sometime around 1964.
2) There were? I never heard of wide spread problems.
3) And, some say the opposite. Everybody has an opinion.
4) This is more of a statement than a question.
5) Why should NSWC Crane want to test bolts?
6) They aren't "MIL-SPEC" for the M16/M4.
7) Bolts made from 9310 have been used on M60s and M249 for many decades without any issue. According to a 1962 report by Watertown Arsenal, 9310 steel was not only more tolerant of heat treating condition variations than the then 'standard' 8620 steel, it was superior in strength. For these reasons the 9300 series steels have been very popular in weapons breech bolts.
1. What I have read led me to believe 9310 was a newer metal.
2.The only issues I have read about concerning 9310 bolts were premature breakage in the AR/M4
3. What is your opinion?
4. Why is Mil-Spec phosphate instead nitride?
5. I am aware NSWC Crane tested the mid-length gas system. Just curious if that type of testing is common for vetting newer potential improvements?
6. Why not?
7. I did not this. Why was C-158 chosen for the M16/M4?
Carpenter 158 was originally developed as a dies steel and when carburized is best suited for application requiring high core strength and subjected to heavy shock and wear.
Carburized 9310 is a very good steel when high core strength, toughness, fatigue, and wear properties are required. It's biggest use is in heavy duty gears and crankshafts.
In 1962 Watertown Arsenal published a report outlining the superiority of AISI 9310 over the "go-to" gun steel: AISI 8620. Shortly thereafter Springfield revised the drawing for the M60 GPMG bolt listing AISI 9310 as the material. When the FN Minimi was designed in Belgium they chose something that was the equivalent of AISI 9310 for the bolt in that as well.
Differences between the two alloys are rather small, the only real difference is the addition of 0.10% of molybdenum in 9310, the phosphorous and sulfur are basically impurities left over from smelting, and Carp 158 would have some of these impurities, even though their alloy listing doesn't mention them. Both alloys can attain core strength in the 160 KSI range and have similar shock, toughness, and fatigue properties
Carpenter 158 Composition (%):
Carbon - 0.10
Chromium - 1.50
Manganese - 0.50
Nickel - 3.50
Silicon - 0.30
Iron - balance
AISI 9310 Composition (%)
Carbon - 0.08 to 0.13
Chromium - 1.00 to 1.40
Manganese - 0.45 to 0.65
Molybdenum - 0.08 to 0.15
Nickel - 3.00 to 3.50
Phosphorous - 0.025 max
Silicon - 0.15 to 0.30
Sulfur - 0.025 max
Iron - balance
So, if all things are equal for the most part between Carpenter 158 and AISI 9310, why only Carpenter 158 for military spec parts? Mainly, the military (specifically the Army) does not now, nor ever did own the design for the AR-15 bolt, and because of this, Colt's Manufacturing controls the material specifications. If the Army felt there was a problem in getting Carpenter 158, or felt there was something significantly better, they could request Colt change the specifications, but that would cost money to: a) research and prove out an alternate, and b) pay Colt's to change their drawings. It may very well be that 9310 is a superior steel for M4 bolts, but the cost to do (a) and (b) are higher that the savings you might recoup from fewer bolts purchased, i.e., no return on your investment. Similarly, Colt's has no incentive to change, carpenter 158 has worked adequately for the last 60 years, so why spend money to fix something not broken.
So why are other people making 9310 bolts?
Carpenter 158 is a proprietary alloy, and only available from Carpenter Technology. If you want some, you probably have to get a few tons of it. AISI 9310 is non-proprietary and available from many different foundries, in smaller quantities, and probably a lot cheaper. Many AR bolt manufacturers make bolts from 9310, and they work just fine and last just as long, but they will never be "proven" until somebody with really deep pockets reaches into those pockets and funds a serious test of the two bolts. And, the only folks with pockets that deep have no incentive to conduct such a test, because they have something that works, either 158 or 9310.
1. What I have read led me to believe 9310 was a newer metal.
2.The only issues I have read about concerning 9310 bolts were premature breakage in the AR/M4
3. What is your opinion?
4. Why is Mil-Spec phosphate instead nitride?
5. I am aware NSWC Crane tested the mid-length gas system. Just curious if that type of testing is common for vetting newer potential improvements?
6. Why not?
7. I did not this. Why was C-158 chosen for the M16/M4?
1. 9310 steel has been around since the late 1950s.
2. I have not heard of 9310 bolts breaking in ARs with any greater frequency than bolts made from Carpenter 158.
3. My opinion is in post #5.
4. Because the drawing originates from 60 years ago when the available methods for nitriding were either expensive, or prone to leaving a thick "white layer" which does not enhance fatigue properties. And as noted in post #5 changing things cost money, so why do it unless you really have to.
5. As noted in Post #5, very low potential return on investment.
6. See post #5
7. For that you would have to ask the materials engineer at Armalite that recommended Carpenter 158® as a bolt material, maybe he/she didn't know about Flexor®, or CX®, and didn't think S-7 would be a good choice.
pointblank4445
04-05-21, 11:04
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?
lysander,
Thank you for the 9310 summary. Quite educational and I appreciate it very much!
Paul
Thank you lysander for continuing to share your knowledge with us on this forum. I know some SMEs have left over the years, and I truly appreciate the folks who've stayed. I hope to keep learning more and more as long as I can.
Sent from my Pixel 3a XL using Tapatalk
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.
Mysteryman
04-07-21, 05:09
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.
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.
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
04-07-21, 14:53
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
04-09-21, 05:05
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.
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".
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-bolt-carrier-group-basics-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
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.
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-bolt-carrier-group-basics-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?
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.
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.
I have a number of reports that stated that 9310 is actually a very forgiving steel to heat treat compared to say 8620 which no one has every accused of being a difficult steel to treat. If fact, 9310 response to thin section quenching is better that Carpenter 158.
And, taking the leap between this statement:
". . . 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 . . ."
and this statement:
". . . 9310 is harder than C158 but it’s also more brittle, it’s fatigue life is also notably shorter than C158 . . . "
Is an unsupportable leap.
First, I am going to take issue with "several elements present in its composition that are detrimental to fatigue", the only element in 9310 that is not in 158 is molybdenum which is not "detrimental to fatigue", the other two elements , as stated earlier are impurities that will be present to some degree in all alloys.
Second, 9310 is not "harder". It is hardened to achieve the proper strength, and that happens to be the same hardness as Carpenter 158, around 36-40 HRc.
And last, I have not seen any study of 9310 that states it has a short fatigue life. In fact one of the reasons it is popular as a gear material is because it can withstand high cyclic loading over a long period of time.
So, stop requoting the myth that 9310 is "harder to heat treat", "is harder and more brittle", and unless you can cite a study that shows 9310 has a poor fatigue behavior, stop that too.
"Low Cycle Bending Fatigue of AISI 9310 Steel Spur Gears"
In a fatigue test of AISI 9310 steel gears the information shown below on cycles to crack initiation was reported. The steel in question was carburized at 1650° F for 8 hours, austentized at 1550° F for 2.5 hours, quenched in oil, frozen at -120° F for 3.5 hours and tempered at 350° F. Since 9310 AR bolts are proprietary, I can't say what process they used to heat treat their bolts, but the above is almost exactly the heat treatment used for the M60 bolts.
https://i.imgur.com/VtyXzDL.png
In "Failure Analysis of an M16 Rifle Bolt", the calculated maximum stress in the most heavily loaded locking lugs is shown below:
https://i.imgur.com/PLqZUOX.png
The red area in the model is 1070 MPa, or around 156,000 psi.
Between these two bits of information, I would say that expecting a 9310 bolt to last at least 5,000 cycles (which is about the earliest point where Carpenter 158 bolts first start to show cracks), is not unbelievable.
Lysander, thank you for all these great posts!
I would add the government doesn't like adding cost to a per-unit item price, whether that is the price of an individual replacement bolt or a complete rifle -- unless they are looking for a specific improvement. I have no idea if there is a price delta between Carpenter-158 and 9310 bolts.
Something else (and I don't know whether or not it matters) to consider -- isn't Crucible the only foundry that batch-makes Carpenter 158?
SeriousStudent
04-10-21, 09:19
I have often wondered the exact same thing. Great question, I'm going to move this thread the AR Technical Discussion, and make it a sticky.
Thanks very much for the data here, it's much appreciated.
SeriousStudent
04-10-21, 09:22
Lysander, thank you for all these great posts!
I would add the government doesn't like adding cost to a per-unit item price, whether that is the price of an individual replacement bolt or a complete rifle -- unless they are looking for a specific improvement. I have no idea if there is a price delta between Carpenter-158 and 9310 bolts.
Something else (and I don't know whether or not it matters) to consider -- isn't Crucible the only forge that batch-makes Carpenter 158?
I remember a conversation with Will Larsen years ago about minimum order size regarding Carpenter 158 steel. It was one of those late night talks as Will was driving across country to teach.
I think you are right, but it was really late at night so I'm not positive. I'll see what I can find out. I recall him saying availability has sometimes been a challenge, due to minimum order quantities.
I also deleted a couple of dupe posts - sorry for the website lagging at times.
I love this thread. Many thanks to the participants. :)
Didn't the M240 replace the M60?
Any idea if the M240 bolts are still 9310?
Didn't the M240 replace the M60?
Any idea if the M240 bolts are still 9310?
The M249 bolt is AISI 9310.
M240 bolts were never 9310. The M240 bolt is actually two parts, the breech block itself, and the locking flap. Both are specified in a Belgian steel specification, but these steels are similar to AISI 4130 for the breech block and AISI 8620 for the lock.
Lysander, thank you for all these great posts!
I would add the government doesn't like adding cost to a per-unit item price, whether that is the price of an individual replacement bolt or a complete rifle -- unless they are looking for a specific improvement. I have no idea if there is a price delta between Carpenter-158 and 9310 bolts.
Something else (and I don't know whether or not it matters) to consider -- isn't Crucible the only foundry that batch-makes Carpenter 158?
It cost about half a million dollars for the Army to change a drawing. The return on investment needs to positive in three or five years, let's say five as it makes the math easier.
A bolt cost the Govt about $40, and let's say they buy 100,000 a year, and let's assume that 10% of that is the raw material. So, in order for this to meet the return on investment requirement, the raw material would have to be 25% cheaper.
Carpenter 158 is not that much more expensive than 9310 . . .
Carpenter Technologies of Wyomissing, PA. (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwieodWcz_TvAhVEBs0KHfd-DlkQFjABegQIAhAD&url=https%3A%2F%2Fwww.carpentertechnology.com%2Fhubfs%2FPDFs%2F2009GuidetoSelectingCarpenterSpecialtyAlloys.pdf&usg=AOvVaw0EORcwTe8J-RmG7CxkhPbQ)
I'm gonna sit right here, be quiet, and learn something new from yall. Thank you all for sharing hour knowledge! This is why I joined.
🙂
I would have to say that 9310 is a perfectly adequate substitute material.
Yet many are sold as some new wonder improvement vs C158. That doesn’t make me trust the company with the other critical processes.
To the OP on Nitride. I’m very much against nitride on any critically heat treated part. The nitride is hot enough to alter the hardness.
Yet many are sold as some new wonder improvement vs C158. That doesn’t make me trust the company with the other critical processes.
To the OP on Nitride. I’m very much against nitride on any critically heat treated part. The nitride is hot enough to alter the hardness.
That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.
That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.
Does anyone have a reason to believe/disbelieve which companies may nitride as part of the heat treating process?
Thanks to everyone contributing. Way outside my lane, but I am enjoying the read.
It cost about half a million dollars for the Army to change a drawing. The return on investment needs to positive in three or five years, let's say five as it makes the math easier.
A bolt cost the Govt about $40, and let's say they buy 100,000 a year, and let's assume that 10% of that is the raw material. So, in order for this to meet the return on investment requirement, the raw material would have to be 25% cheaper.
LMT spent a lot of their own money to offer the world a super-duper improved M16/M4 bolt and carrier. Per Karl Lewis, the improvements don't provide overwhelming superior performance or extended life over the legacy bolt and carrier group -- or, rather, enough for the .mil to replace all they have, and to start buying them as replacements vice what's tested, spec'ed, and in the system and drawings.
https://i.imgur.com/c4aREwc.jpg
That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.
So is there actually a way to get the benefits of a hard nitride surface while still retaining the desired core hardness? On a bolt, specifically.
I had the impression that the nitriding is done in a high-temperature (~1000 F) salt bath after the primary heat-treat, and that’s hot enough to temper the core down to something softer than spec. How can this be avoided? Nitride first?
Apparently pre-2005 there were enough M16/M4 C158 bolt failures to conduct these tests.
Failure analysis of the M 16 rifle bolt
V. Yu, J. Kohl, +3 authors M. Veach
Published 2005
Recently, there have been several occurrences of failure in the bolt of the Ml6 rifle at a United States Army installation. Near the failure location, the bolt was subjected to repeated loading as the Ml6 was fired. In order to determine the stress distribution of the bolt due to the firing process, a geometric element analysis was performed using ProMechanica . The fracture surface was examined using both an optical stereomicroscope and a scanning electron microscope in order to determine failure initiation and failure mode. It was discovered that the fracture initiated at a localized corrosion pit and propagated by fatigue. A controlled experiment was conducted where 1800 and 3600 rounds were fired using new bolts. After 1800 rounds, a region of wear was observed near the site where fracture occurred in the failed bolt. After 3600 rounds, a notch was observed in this wear region. This suggests two possibilities: firstly, exposure of the base metal may have facilitated the formation of the observed corrosion pits; and secondly, the presence of a notch may facilitate the fracture of bolts in general. In addition, Vickers microhardness profiles were taken on cross-sectional areas near the fillet region and 10 mm away from the failed locking lug. Disparities between microhardness profiles near the fillet region and 10 mm away from this region revealed that the bolt may not have been uniformly case hardened. Published by Elsevier Ltd
More info and diagrams at link
https://www.semanticscholar.org/paper/Failure-analysis-of-the-M-16-rifle-bolt-Yu-Kohl/566b1271350753d0655493ae05820f84258e20ed#extracted
Does anyone have a reason to believe/disbelieve which companies may nitride as part of the heat treating process?
Thanks to everyone contributing. Way outside my lane, but I am enjoying the read.
So is there actually a way to get the benefits of a hard nitride surface while still retaining the desired core hardness? On a bolt, specifically.
I had the impression that the nitriding is done in a high-temperature (~1000 F) salt bath after the primary heat-treat, and that’s hot enough to temper the core down to something softer than spec. How can this be avoided? Nitride first?
In order to achieve the required strength, you can't just plunk a piece of steel that has been tempered below the nitriding bath temperature, that goes for a nitrided Carpenter 155 or a nitrided 9310 bolt. As to "how", you will have to discuss that with a nitriding specialist.
Yes, as to how, you would have to discuss that with someone that handles nitriding.
I'll reach out to H&M Metal Processing tomorrow.
http://blacknitride.com/about-us/
Solving metal problems for over 70 years.
Through the H&M Blacknitride+™ process, or Ferritic Nitrocarburizing, we can improve the operational capabilities of your components, solving wear, lubricity and corrosion resistance problems. Whether one ounce or 4,000 lbs., orders are filled with the precision and quality for which we’re recognized. Our stringent quality testing process before, during and after treatment ensures the integrity of the product according to the requirements and specifications of its customers.
Our current facility is ISO 9001 certified. We’re equipped with comprehensive metallurgical laboratories, providing all related research and development for all operations.
Founded in 1946, by Ernie Hedler and Art Marble, our services included hardening, flame hardening and black oxide coating. In 1950, the Korean conflict brought considerable growth to H&M through the processing of tank tracks, breach blocks, brake discs and many other products used by the U.S. military and its allies. Over the years, the company continued to grow and, in the 1980’s, expanded its heat treating capabilities to include Black Nitriding. Our operations have expanded and moved with one goal in mind — to give our customers best-in-class service.
LMT spent a lot of their own money to offer the world a super-duper improved M16/M4 bolt and carrier. Per Karl Lewis, the improvements don't provide overwhelming superior performance or extended life over the legacy bolt and carrier group -- or, rather, enough for the .mil to replace all they have, and to start buying them as replacements vice what's tested, spec'ed, and in the system and drawings.
https://i.imgur.com/c4aREwc.jpg
Low Plasticity Burnishing of the lug root fillet has the possibility of doubling the fatigue life, and allows the use of existing barrel extensions.
The big plus of the LMT bolt is the extractor spring(s) are a more sensible length to coil ratio.
That would depend on if the nitriding is done as an afterthought, or does as a integrated part of the overall heat treating process.
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.
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?
Mysteryman
04-15-21, 19:01
The hype stems from the amount of circulated misinformation. Even from industry insiders and so called industry "professionals".
exactly..
Anyone have bolt lug wearing or shearing with their 9310. Seems it's more common than on a C158 bolt.
Evil Black Rifle
11-06-21, 11:17
.... 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.
duroSIG556R
11-11-21, 06:45
When were 9310 bolts first introduced?
Early on there were some issues with properly heat treating that led to breakage. Has that since been corrected? If so when?
Some say a properly heat treated 9310 is better than mil-spec C-158?
C-158 bolts are available in both phosphate and nitride, it appears all 9310 bolts are nitride only?
Has Crane tested 9310 bolts with the latest heat treatment processes?
Are there any drawbacks to a properly heat treated 9310 bolt?
Are 9310 bolts still considered unproven?
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.
The big plus of the LMT bolt is the extractor spring(s) are a more sensible length to coil ratio.
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.
chamber143
11-12-21, 06:53
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.
Mysteryman
11-14-21, 03:26
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.
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
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 (https://www.65grendel.com/forum/showthread.php?13760-65G-Bolt-face-Depth-Infographic&p=152007&viewfull=1#post152007):
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.
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
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.
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.
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.
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.
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.
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").
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.
Seeing as the material is listed as a critical characteristic, it's going to take a little more than, "Yeah, let's do it!" Mainly, because I would think the part number would roll (you would have to have completely new heat treatment requirements, as 9310 requires different heat treatment).
Changing a non-critical pistol grip panel from Nylon 6/6 to 6/12, or its color, it a lot easier.
There is also the case where the contractor calls you up on the phone and says, "Oh, by the way, we've changed the material of the spring guide from aluminum to plastic. Hope you don't mind." Then the Govt has to show a technically valid reason why that change is unacceptable, or just accept it. One of the downsides to not owning the design.
Seeing as the material is listed as a critical characteristic, it's going to take a little more than, "Yeah, let's do it!"
I get that. I was using the Army saying it as a "for instance".
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