I've been around AR's, M-16's and M4's for years in the military and civilian side, and I've never seen a bolt failure. It was only a myth all these years, thanks for showing the results of bolt failure. Also, though we feel attacked on watching movies while cleaning guns, that's a great point to consider as we could miss a small detail that could lead to a catastrophic failure at the most inopportune time. Thanks for a great video
Retired Army, 11-B. I never seen a bolt failure, but every time they forced us to oil our bolts prior to turning our weapons in, they'd jam every time after we checked them back out. The oil would cause dirt and sand to stick to the bolt and cause jamming.
One thing when they apply the NiB coating is that they need to activate the hardened surface of the steel with hydrochloric acid, causing a high probability of hydrogen embrittlement. If they’re not baking for the hydrogen embrittlement relief after the plating process, you will get fractures in the high strain areas prematurely. JP bolts have larger radii on there bolt logs to reduce the stress risers.
I feel like having an AR is the same as having a bucket of survival food. It makes you feel better for having one, but deep down you know it won't last, and you hate to think that one day it may be all you got.
iv'e had mini 14's for 35 years, i honestly can't remember a malfunction. newer 580 series are much more accurate than the older 180 series. steel barrel gets 1 1/4 inch group at 100...i live in one of the worst climates on earth. ive tried ar's, but when the shtf i'm taking a weapon that goes bang every time. and if a mini ever does malfunction i can get it back on line much faster than a AR. haven't cleaned my mini 's in ten years, shot 60 rounds yesterday. the older one has a few thousand rounds through it...this weapon is so underated...
When you shoot enough, you will start to see failures. I broke my first bolt at over 10,000rds on a CLGS 16" upper, shooting 300-500rds per day every weekend, and competing with it.
As a Metallurgist with some knowledge of Failure Analysis and Fracture Mechanics this was Fascinating. At the risk of being a know it all the failures all appear to be Brittle failure and at obvious stress concentrations. There appears to have been little to no attempt made to reduce the stress concentrations. In addition case hardening exacerbates this problem
USAF and US Army did a study on what was causing bolt failures on the very early rifles, namely Colt 601s and 602s. Originally, the entire Bolt Carrier Group was hard chromed, including the bolt. They were cracking bolts at the cam pin hole and shearing lugs, found to be due to hydrogen embrittlement from the hard-chroming process. They changed the metallurgy and phosphated the bolts, and improved process to strengthen them. Worked fine in the M16s with Rifle-Length Gas, but we started seeing issues again once SOCOM got the M4A1 and started putting them through high volume shoot sessions. Canadians made a much better bolt carrier group with the Diemaco rifles and carbines. US Mil-Std calls for a certain alloy, shot-peening, and 100% non-destructive testing of every bolt with High Pressure Test proof loads. That's what weakens bolts. ARDEC did a study with a new liquid CNC burnishing process that doubled bolt life from 13,000 to 26,000rds in compressed, high-volume shooting sessions.
Why it took so long for me to discover this channel and the fact that it is not 1M+ subscribers is beyond me. Every video is so helpful and greatly appreciated.
Thanks for another great upload. School of the American Rifle should be required viewing for anyone utilizing the AR platform. Information on this channel is priceless.
With the Nickel Boron bolts, potentially very little firing was done before failure because of hydrogen embrittlement issues with that coating. I’ll bet they aren’t made from C158 either
@Nicholas Armock They're supposed to be absolutely trivially easy to clean, carbon not sticking hard to it at all. I never knew they were suspect to brittleness though.
I had a bolt out of an older Bushmaster crack, but not break. Rifle started to jam, a lot. I still have it in my parts drawer. How is it that this page only has 32.9k subs? This is one of the most informative pages on YT. Until I found this page, I had no idea most of these gauges and tools existed.
The one part on Bushmaster rifles that was good was the barrel. They really had things dialed-in with the company that did their chrome-lining. The rest of the parts were mediocre at-best, many of them garbage.
Thank you for the educational examples. I don't shoot a lot but thought I had been around the block at least a little bit and never even knew that could happen let alone multiple examples
I am a former Army Sergeant and company armorer. We never replaced parts unless they broke, or if an issue was reported to us by the issued operator. The problem is the FNGs (
Thank you for your service and I can understand. I worked for my city, right out of trade school, and saw real quick how messed up government bureaucracy is. Seems no one cares about improving the way things are done unless told to. The lack of initiative shocked me. In talking with former military co-workers, at another job, it sounded like it was similar in other levels of government too, in general.
I worked at a GS level shop before they turned maintenance into 100 percent contract BS. I worked in the electronics section but we had an armament section as well as DS/GS level vehicle repair as well. If you know about diesel truck repair, you probably know what a magnaflux machine is: its used to find cracks before they're actually visible. I got to see a number of M16/M4 catastrophic failures that could have been prevented by routine magnafluxing (I guess its called MPI when its used for gun parts?). When you look at these things under magnification, you'll see that there are shiny parts of the crack, which means that they cycled probably thousands of times after the crack had started forming but before it was noticed.
Man, making have to breakdown my gear and actually inspect it! _This is my rifle, this is my gun..._ Do so love learning about the nuance and intricacies of the AR-platform. Left more and more in awe of designers and engineers who once upon a time did things with just pen and paper.
That makes sense. Isnt that ammo loaded at several thousand psi higher than other 556? Also, i went to the bill moran school of blades smiting a few years ago i assume thats what your profile pic is referencing
Bro, i just want to thank you.. im an avid firearms enthusiast.. mostly pistols... Ive been a pistol guy my whole life.. i keep all my buddies 1911s up and running, all their and my glocks , czs and clones ect.... Im a pretty good pistolsmith too.. so i know the lingo, the concepts, and all that comes with it... I finnaly made the jump into the ar platform last with with a bonus check from work.. purchased a used m&p15 lower, ( got it for 20 bucks because the trigger guard ear was broken.) Bought. Daniel defense intrgrated triggerguard and grip to hide that, and a parts kit.. the lower was pretty straight forward... I had all that assembled in 20 minutes . My problems came with the upper, and lining up the gas holes, and the gas key with the tube itself. Had a little overhang on my feed ramps too.. not enough to fool with considering i learned in your video that its not neccisarry unless my rounds contact the lower reciever ramps first.. in which case theres a problem... You videos helped me go from nothing but parts, to a functioning , accurate, beautiful rifle i have the pride of saying i built with my own hands .. thanks for you passion man..
This is a very good video, I have shared to my own group. Inspection for cracks like we see here should be part of any cleaning or maintenance procedure
i feel like a solid way to prevent or prolong the issue from happening would be to radius all hard edges like around the extractor and cam pin hole and firing pin pass through on the cam pin radiused/chamfer greatly strengthens the edge. hard edges inside high stress parts are know failure points. can be found in high torque/pressure situation like in prop shafts in both aviation and nautical vessels. Kieth over at turn right machine works dropped that info on the world during one of his vids. really helped me understand the importance of breaking the edges and avoiding cutting hard edges in the depths of something like a keyway. or in this case an extractor cutout. if u want to do some redesign i would recommend doing an extractor cutout in the radiused bottom with round tip ball mill and making an extractor with a matching surface and redoing the locking lugs with a radiused edge it will reduce lockup surface but fairly certain it would still have a % over safe operating peramiters.
deffo agree to that on most high stress area..I fly RC an there is a type where the motor an prop is in a slot in the middle of the plane an if you cut the slot straight you get stress cracks but cut a radius cut no issues at all... unless you crash it..but even then very rarely cracked
I agree. I'm guessing the original design was somehow a consequence of manufacturing or inspection limitations of the 1950s. It's probably easier to make and inspect mating parts with rectangles than it is with arcs. Personally, I don't particularly like the 7 lug design either. For one, they're hard to clean. More relevant to this video, any sort of uneven load will concentrate the force on 1/7th of the locking mechanism, which is bound to cause stress failures eventually. These examples show us pretty clearly that the lugs next to the extractor routinely face more force than the other lugs. I own a rifle with a more modern bolt, and the designer went with a 3 lug design (essentially a triangle with rounded off edges). The lugs are much beefier individually (probably cumulatively as well), and there are very few sharp corners. The AR platform is great, but it also has its roots in the 1950s AR-10, and after 70 years, it would be nice to see some incremental improvements become the new standard. It's really not that hard to design a sturdier bolt face that's easier to clean.
Wow. Lots of comments asking for specific user history of each bolt. It doesn’t seem like that was the purpose of this video. This video does an excellent job showing how a bolt fails (weakest points) and where to inspect for damage leading to failure. That’s all. Everything mechanical can fail, and can fail early in some conditions, all you can do is buy quality components (primary and spares) and do your inspections.
It makes sense that the lugs near the extractor would be the most prone to break, because there is already one lug missing due to the extractor. I’m surprised that the design didn’t incorporate different lug geometry on either side of the extractor to make them stronger/ even out the forces, but they probably didn’t fail often enough to bother. It certainly couldn’t be changed at this point.
In the early 1960s, they experienced enough cam pin hole cracks to study the problem. It was determined that hard chrome was causing hydrogen embrittlement, so they changed the TDP to phosphated bolts. M16s don’t normally break bolts since port pressure is so much lower than CLGS variants. The bolt isn’t subjected to the same torsional loads during unlocking with RLGS and correct ports.
My two sons and I shoot NRA matches, FTR and Service Rifle. One thing I've learned over the years from having to stop and repair rifles during the middle of a match, I keep a spare of almost everything in the tool box.
I was issued an M-4 while in gov’t service. The bolt broke while shooting frangible ammunition in a shooting house. Frangible ammo pressures have a reputation for breaking bolts. It was common to carry a spare bolt inside the pistol grip of the M-4. Never did that for any other rifle.
always been an AK guy just got into ARs been watching all of your videos it amazes me at how many failure points the AR has never seen anything like this with com block AKs
That has long been my comment. How many AR dudes carry spare parts kits (especially bolts) ? Now what's the last time you've heard of someone carrying a spare AK bolt with their AK at all times lol? There's countless companies selling super mega improved AR bolts, why is this? Is it a poorly designed point of common failure? Or are AR fanboys often gullible gear queens that are easily separated from their money? Personally, I think it's a mixture of both. Just read Arfcom discussion boards sometimes to see the often illogical gear queen group think in action.
Careful inspection while cleaning made me see a safety flaw in an after-market Glock slide. The firing pin safety worked the first time each time the slide was assembled but it would not reset consistently. Extremely good advice!
That's really interesting and disturbing at the same time. Most people think of bolt failures as things that happen to others, but seeing a table full of them screams "check your bolt and lugs thoroughly when cleaning your rifle " That brings up an interesting thought- regular cleaning isn't a "thing" like it was when I was in the service. Modern AR rifles function very well, even when filthy, but if you don't clean it, are you checking and inspecting it? I'll be far more attentive going forward
Having spent some time in the Army when I hear infomercials saying " built to military specs!" I know most of the time it's junk. Bolt failures with even a brand new kit is very common in the service. It's funny I've never had one on my custom built rifles with non- mil spec bolts, but a great reputation have not failed with a ton of rounds.
I had a bolt lose a lug and break at the cam pin hole in my issued M4 while i was in the Marine Corps. The most common failure I experienced however was with the burst trigger assembly, I had 3 disconnectors break on me. it was so bad it was funny until i was finally graced with a new M4 from the Army.
There must be something to it that the lugs that failed are all unsupported metal on one side. So inspect all lugs for damage but the lugs next to the extractor are the most likely to fail
Great video! Nice to actually see what can happen. Definitely always good to have spare parts on hand, including populated bolt heads and even entire bolt carrier assemblies and more.
Oh great, I've got a Raineer Arms bolt carrier group... I'm glad they have a lifetime warranty... but also, I'm using it in a 20 inch standard DI gun... which hopefully isn't as stressful for it as say a shorter gas system... Yeah, what would be the best bolt to keep in my spare parts kit in the back of the rifle.. possibly... the JPE Enhanced bolt made from SAE 9310 is a good choice??
JP is great but LMT enhanced is best imo. LMT enhanced has had no failures so far as I am aware. KAC is also up there with the LMT but I give the LMT a slight edge.
I broke a bolt where the cam pin enters. It broke in two. It was off a American tactical 7.5 pistol. It was the first ar I bought and had the polymer upper and lower. The upper broke at the take down pins 300 rounds in. The bolt broke at 900 rounds. I then sold it and bought a bcm and haven’t looked back.
I'm new to your channel, videos are very well done, informative, and thorough. Would like your opinion on one thing though, lubrication of an AR especially the bolt carrier group. There's a lot of videos on lubricating the AR (wet minimal and everything in between). My question is your thoughts on lubricating the AR, especially the bolt and where? I'm pretty sure you've seen most everything and the effects. Thanks
Have a Aim Surplus nib bolt that sheared a lug off next to the extractor last night after I cleaned my rifle and sent the bolt home.I pulled back on the charging handle and it wouldn't budge so by having to motor the gun to get the bolt to unlock off came the lug. Working with them now for a replacement but this bolt had less than 600 rounds fired. Passed head space clearance when I put the rifle together and it cycled well with no failures till this happened. So you never know, heat treat, etc etc...
The lugs will always fail near the extractor first (unless there is something really wrong with that bolt). The reason is its design and simple physics. However, the bolt will run fine with one or two lugs missing but will lose more lugs soon after the first ones (not that I recommend using a damaged bolt for obvious reasons).
@lifepolicy what causes a lug to sheer off though? I had the same thing happen and can’t find an answer. And no it wasn’t dirty. I bought a new bcg and im worried about shooting in case it wasn’t the bolt that was the issue.
Back in the mid to late 1980’s, the AR-15 was MY DREAM GUN! An older military guy with an FFL who hunted with us was always breaking out his M-16 and doing a couple of mag dumps. I wanted an AR-15 so bad, I just couldn’t imagine they would be so affordable or obtainable as they are these days.
I had a Daniel Defense bolt crack and look exactly like the first example you showed. Shooting out of a 10.3" DD barrel (unsuppressed) and cracked at ~5k-7k rounds. I was a little disappointed being that it was a DD BCG.
LMT enhanced is generally recognized as best overall bolt, I have yet to hear of a single failure with them. Usually gets run in a kac sandcutter bcg by most guys to cut down on cost a bit over some of the more expensive carriers. Best bang for buck complete bcg would imo probably be a SOLGW. Good bolts, carriers, carrier screws, etc.
Never heard of these failures and never saw these failures. Its very interesting though. I have no idea how many rounds I have through an M16 M4 or AR15 but it may be well over a million by my best guess. Like I said.... I never saw this. I am extremely curious about it now.
From my perspective the breaking of the bolt is a construction problem, not a material problem it just has no way to go, stress peaks where the edges meet, the outer layers are too rigid and the crack starts. Once it starts it'll find it's way. At 0:55 and HD setting, the failure progression is visible (moving and seating). If that breakthrough (probably for the cam to rotate the bolt?) was oval just at the top and bottom, it would less of an issue. But who wants to build that? Replacements are cheaper that way. Very interesting video. You got a good sample size with all the ARs you work on.
Great reminder about proper inspection. I have certainly been guilty of hustling thru a cleaning occasionally,,. Just wanna "get it done", gotta dedicate more time, be more thorough. Great heads up 👍🇺🇸👍
Wow! Great video. I have several questions if I may. > Why are the lugs adjacent to the ejector the ones directly affected? You mentioned government contracts M4/M16. > You happened to have the makes? > Is overgassing possibly the culprit? Thanks in advance.
So what is the story and history on each of the samples you have? Having a piece of paper somewhere in my home that says I'm an engineer, anything mechanical can and will fail, and with the number of AR's out there you will always get a bad one every now and then. Looking at the collection you have, I'm curious on the history of the samples. If you think about it, I could load up some .223/5.56 rounds with a pistol powder like 700-X and get the things to fail, but that would be the result of me being stupid. Of course on the other side of this, you have a lot of them that failed which could be a problem if they all lived the same life and have the same story, but the devil is in the details when it comes down to finding a pattern and a problem that needs to be solved.
I have no idea where the AR-15 bolt was not redesign long time ago. It seems to be the weakest link in the system next to the gas too. Slightly beefier camping whole and locking lugs would do wonders
Dude you must’ve been military or someone who was military who really knew their shit taught you this . When you demonstrated with the firing pin how it doesn’t sit and you had to push it in forcefully , identifying that it may have a light banana curve bend . That was genius .
Surprised your comment was the first one on keeping 'spare' parts on your person. Without that bcg, your rifle is just a fancy piece of metal and plastic....
Andy idea on cause of failure? Bad design, poor maintenance, bad casting/ machining? It would be nice to know if there’s anything we can do as the end user to prevent the failures or some manufacturers to avoid.
Very interesting, maybe some info on typical round counts before failure, or other reasons/causes of bolt failure. Is this something that is 'normal' for the guy that fires five or seven hundred rounds a year through a cheap Ruger or Smith AR??
Good idea to have a spare bolt for every AR you have and a couple extra BCGs. Ive never seen one fail. But when you cant order spare parts for whatever reason you can rest easy knowing you can get your AR back into service.
