User Panel
Posted: 8/24/2005 8:42:51 AM EDT
I've had this excellent document for some months now. I wanted to share it with all of you. Sorry it took so long, but I've been too busy to be around much lately. I forgot where I attained it, so I am hosting it myself. Please right-click and "Save as" or I may have to take it down.
Department of Civil and Mechanical Engineering, United States Military Academy, West Point, NY - M16 Bolt Failure Analysis This document clearly shows that A LOT goes into making a bolt properly. Not just HPT/MPI. If it is not heat treated and case hardened properly/uniformly, the finish can wear exposing base metal. This allows corrosion and pitting to occur, which in high stress areas will allow a crack to form and propogate from this point. I've done the how long can it go without cleaning thing on my "experiments" rifle. But on a rifle that you trust your life too, you really should clean and relube (atleast the bolt) as soon as possible. On occation closely inspect the high stress areas of the bolt (especially where the extractor rubs near the rear of the lugs on either side) for exposed base metal, corrosion and pitting (use a magnifying glass). This may or may not be enough to detect it, but it is worth a try. Lastly, perhaps this will data will give rise to new rust+wear-resistant materials and/or coatings for bolts? Or perhaps the remergence in popularity of old coatings (hard chrome)? I have heard through the grapevine that manufacturers of bolts for the .mil were put on notice to pay extra close attention to the heat treat/case hardening of their bolts and that this process was revamped with closer/extra QC (this was some years ago, after a similar study) to ensure uniformity of proper hardness. All current bolts (and those from the past few years) from .mil manufacturers should have nearly perfect case hardening. |
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+1 Thanks! |
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Did you unzip it first? |
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_DR:
I'm do not believe it is proper to post their work, names, e-mails and phone numbers on this forum in such a manner without permission (spam/data miners, etc.). At the same time the document shouldn't be posted w/o credits. Also your post is missing all the excellent figures/pictures that really visalize everything for the reader. I know your intentions are only good, but for the reasons stated you should probably delete the reprinting of the material in your previous post and just let everyone download the work in its original form, read it and see the figs/pics that go with it. Windows XP has a zip/unzip utility built in. For those with previous versions, free zip/unzip tools can be downloaded on the internet from Download.com, or found by google.com. For those that don't have a fully fledged copy of Microsoft Word, they can download the viewer here: Microsoft Viewers |
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What about now? edited names/numbers out, retained credit for institutions responsible. Added tables/figures in sequence. Just thought that since this is all funded by taxpayers dollars and is not classified that it was therefore public domain. maybe make it easier for those less computer savvy to see it. This would actually be an excellent article for the AR15.com articles section. However I understand your concern and if you wish I will delete my entire post. Just say the word and it's gone. _DR |
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It would be acceptable to me now if it was my work and now their phone, email, etc. is safe(r) from automated spam/data mining tools so I say leave it and see if anyone complains. Thank you _DR.
ETA: Hmm, actually could you add their names back? The more I think about it, that should be ok. Thank you. |
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Thank you for making it available. Name credits restored per your request. |
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I appreciate all the thank you notes, but these guys did the real work. I'm just making putting it up for download. Besides, this is really just returning the favor for all the help I've received from all of you on the forums. Keep the free flow of information going! THANKS TO ALL OF YOU.
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Many thanks for posting this very interesting and useful data.
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It would be neat if we had a study of similar methodologies pertaining to bolt breakages at the cam pin hole. I suspect the failure mode is often similar:
Base metal becomes exposed, corrosion pitting occurs, a crack forms and propogates from its origination point. CLEAN (not too much!) AND RELUBE YOUR RIFLE! |
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I cannot believe minor corrosion could cause such a catastrophic failure. We have used these things in jungles for 40 years in monsoon conditions. Something else is in the mix.
As far as the failures per year at the installation graph, how much more traning is being conducted today vs 1999? More rounds fired=more failures. |
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Inproper, non-uniform case hardening. I have inspected a bolt (Colt) with over 3k rounds on it in the area where the extractor is said to cause wear and there is none. Why? Because the case hardening is uniform and correct. It is possible that for a small number of years in the late 90's some batches of bolts were not being properly, uniformly case hardened. This allows the surface to wear and the base metal to be exposed, allowing corrosion pits to form if exposed to the elements. Corrosion pitting in a high stress area that is already at the max in its' ability to hold up against said stresses as it is, can be expected to cause failures. Notice the broken specimen was not uniformly case hardened. Now if it is properly, uniformly case hardened, it might still wear, expose base metal, corrode and break but later (say 10-20k rounds) instead of showing wear at as little as 1,800 rounds. I've seen many bolts with broken lugs on either side of the extractor and the path of the crack looks almost exactly the same. The origination point is likely the same. The failure mode is likely to be the same, but it just happened later in the bolt's life. This coincides with the rumors I've heard about manufacturers being put on notice awhile back about case hardening procedures, which were supposedly revamped along with the QA processes that go along with it to ensure every bolt is properly, uniformly case hardened. Basically it has been getting a little extra attention. HPT/MPI is not the only QA a bolt goes through. |
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Likely case hardening would occur after shot-peening to provide the most robust surface finish possible. Interesting that case hardening is a process used on small arms since the mid-1800's that is still proving it's value in the space age.
I have always believe that an addtional persistent lubricant such Tetra grease applied in a thin layer to critical high-heat, friction bearing contact areas such as the cam pin and cam pin hole can make a difference when a bolt is pushed to perform under extreme use. This data does not seem to contradict the idea that stress and heat reducing lubricant may stave off failure at least for a time. Now what would be very interesting is a similar study done with a gas-piston impinged system where the temperatures of the bolt group are typically far lower than with a direct-impinged system such as the M16, with extended operation. |
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I had some tests run on some failed 50AE bolts back in the late 90's and the results showed that the carburized depth (case hardening of the surface) was all over the place. If the carburized depth was too deep, the lugs would break off. If it was too shallow, the lugs would curl inward. I did not see a chart showing the hardness at various depths around the bolt in this analysis. When they analyzed my bolts, they sliced very thin cross sectional waffers through the bolt body and analyzed the hardness at various depths. I am sure adding some pitting to the surface doesn't help things either.
The bolts are actually heat treated to the core first, as hard as Carpenter 158 can get. Then they are carburized, to harden the surface. But if you over do it, they will get harder, deeper into the core. I know because they screwed up and over carburized 100ea of my bolts and scrapped the whole lot. That sucked. Tony Rumore Tromix Corp |
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It is a good read, if you are into such thing, but one thing I notice is that the photographs apear to be of old worn M16A1 bolts rather then M16A2 bolts.
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Another odd thing is the graph. It does not include info on the age of the weapons, or the size of the pool. First thought I had was that their rifles had reached the end of their service life, duh. About as informative as the pirate graph chart with temperatures.
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Anl like I said before, what about the change in optempo due to the global war on terror? How much more training has been going on per annum since 9/11?
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Hey, me again, still thinking out loud. I got an explanation on the pictures of busted M16A1 bolt, maybe these are bolts out of M16A1 remanufactured as M16A2's. The upgrade kits come less bolt groups.
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Yes, we are on the same page, the info left out is important in understanding the large number of failures, and the pronounced increase in occurrences. There is no mention that the bolt pictured is 40 to 23 year old. Just the same the info on how they fail is very interesting. |
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This is quite an interesing post......tagged for further reading.
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Fortuantely the bolts redundant locking lugs provide a generous safety factor. Still the increase in bolt fractures indicates a QC problem. No wonder these are like hen's teeth today.
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Still, a broken bolt lug can be caught in the barrel extension's locking lug recess or down in the trigger assembly and jam things up good. Ekie, excellent observations re: M16A1 bolts. I can't believe that didn't register with me, I usually don't miss things that obvious. |
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Well, I have had that report for over 6 months, and it was not until your thread that I noticed that the failures were dealing with M16A2's. Am now thinking, what, that ain't no M16A2 bolt. |
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Bolt lugs have a radius cut on the corner. 1960's and 1970's bolts had the radius cut in such a manor that it left a 45 degree mark in the bolt body. Later bolts lack these cuts in the bolt body. The busted bolt in the picture is an old bolt with the cuts. We talked about this subject here: www.ar15.com/forums/topic.html?b=2&f=29&t=146824 Need to take a closer look, but my first impression is that the busted bolt pictured has been refurbished. Looks like it was rusty and pitted at one point, and then refinished. |
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Wow! In some of the failed bolt pictures you can actually see how deep the casehardening is! That's metalurgy that just about anyone can understand! And the stress locations on the bolt lugs makes a lot of sense-and that's why EVERY TIME I shoot I clean, inspect and lube the bolt (along with the rest of the rifle-I have a flat spot on the back of my head from "reinforcement" for doing a good job at rifle cleaning!), paying particular attention to places like the lug roots and the recessesed bolt face.
Thanks wyv3rn for the wonderful document! |
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Well.. I'm trying but I don't see that. |
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could also be poorly done Parkerizing, you'll often see surface etching similar to that pictured.
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The lack of sharp edges gives the appearance af a second park job.
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