Hey all-

I am curious to know what parts people here have observed to break (or seen obviously about to break) on hard use ARs. When your rifles have seen high round counts at occasionally high speed fire, what are the failure points?
The usual suspects are extractors, bolts, bolt cam pins but I would like to hear some real world experience with actual failed parts.

I am not interested in the published estimates for preventative maintenance or your personal "I change xxxx every xxxx rounds or xxxx years, whether it needs it or not".

I am especially interested in stuff that would surprise us. Gas tube failure? Gas block? Cracked barrel nut?

What kind of oddball stuff have you seen or heard about from the guy who saw it?

I would love it if Mr. Jones and any of the MOAC-R students would chime in and reveal how their rifles fared in that epic class/torture test.

Bruce

quote:

know what parts people here have observed to break (or seen obviously about to break) on hard use ARs. When your rifles have seen high round counts at occasionally high speed fire, what are the failure points?
The usual suspects are extractors, bolts, bolt cam pins but I would like to hear some real world experience with actual failed parts.

I am not interested in the published estimates for preventative maintenance or your personal "I change xxxx every xxxx rounds or xxxx years, whether it needs it or not".

I am especially interested in stuff that would surprise us. Gas tube failure? Gas block? Cracked barrel nut?

What kind of oddball stuff have you seen or heard about from the guy who saw it?

I would love it if Mr. Jones and any of the MOAC-R students would chime in and reveal how their rifles fared in that epic class/tortu

For me, Bolt catch/release lever. I think I have replaced more of those than any other thing.

there is a gun / machine gun rental facility in Las Vegas. Battlefield Vegas. they probably have one of the most extensive 'high use' selections of firearms in the country.

this question was put to them and one of their armorers posted this on another board. from a very long thread there that started in 2015.

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Hi Folks,

A forum member asked me if I would give some insight into how our M4's handle on the range because I've started threads on the AK's, pistols and .50 Barretts.

Here's a little background on what we do. We operate a high-volume range in Las Vegas. You can't bring your personal weapons in and rent lanes for an hour. Customers use only our weapons and our ammo. We only use factory new ammo and zero reloads. We keep maintenance log on EACH and every weapon to include cleanings, parts replaced and any other issues that need to be noted. We shoot approximately 400,000 rounds down range each month and the numbers have actually gone up a bit for May and June. Tourists get to shoot everything from Type 99 Arisaka's, M1 Garand C and D's, MP-44's, G43's, M2HB's, 240's, 249's, MG42's, MG34's, M-14's, Luger's, Swedish K's, M203's, M79's and you get the point. Some weapons are very rare historical weapons that rarely come out of collections or museums and see the light of day.

Here are some "facts" about OUR experience with M4's on the range.

- Some of our M4's have well over 200,000 rounds down range. Barrels have been replaced, gas tubes have been replaced, BCG's have been replaced but what sets it apart from the AK47's is that upper and lower receivers continue to function. AK's get to about the 100,000+ round count and rails on the receiver will start to crack. It's an easy fix with tig welding but they crack. We have yet to lose an upper or lower receiver from cracking.

- We get about 20,000 rounds out of bolts before we start experiencing issues. The headspace gauge will start getting closing on NO-GO but not close on field. We will lose a lug on the bolt. The bolt will start skipping over rounds in the magazine and fail to insert a round. We use LMT and Daniel Defense bolts and some will actually go longer but at about 20,000 rounds is when we will start to see issues appear.

- Gas tubes will erode away at the FSB after 12+ months

- Charging handles will "stretch" allowing the locking lever and spring to fly out

- Hammer pins and disconnectors on the 8.5" full-auto's will break after approximately 4,000-5,000 rounds regardless of the buffer weight

- We have yet to lose a single flash hider as compared to muzzle brakes on an AK-47. The muzzle brakes will literally split in half, looking a like bird with his beak open and go flying down range.

- We no longer use ANY piston conversions or factory pistons guns with the exception of the HK-416 "knock-off" TDI upper. I purchased a FACTORY brand-new MR556 and it started keyholing after only 10,000 rounds. I was SO pissed because I spent all that money on the gun and it couldn't last 10,000 rounds. I had barrels from before we even opened the range with 1,000's of rounds on them from J&T Distributing (chrome-lined) that didn't keyhole well into the 80,000-100,000 range. I don't know who makes or made the J&T barrels but I was so pissed that actually wasted the money on a MR556 and that's all I got from it. I purchased two of the 14.5" TDI knock-offs approximately 6-8 weeks ago and they have been on the line daily with ZERO issues. I only purchased them because people will come in specifically request the "416" and even they've never handled a weapon their entire lives, they KNOW that the top half isn't the "416 like in COD/MW".

- USGI mags have outlasted all of the other brands. We use UGSI (Brownell's with tan follower) and on a mag for mag basis, they have outlasted Pmags and a few of the other mags that we get from mfg'ers with new weapons. We don't have to worry about various generations with different weapons like the MR556, SCAR, F2000, Tavor or a couple of others that use AR15/M4 magazines.

- Cleaning bolts and carriers is such a pain in the ass as compared to our AK's, G36's, SCAR's, ACR's and most other platforms. We throw them in the ultrasonic cleaner filled with Simple Green (EPA, OSHA and disposal concerns for us) and they never full remove the carbon from the bolts. The armorers spend so much time cleaning them and keeping all the parts together as compared to most other platforms.

- The only piston system to last on the range so far is the HK416 and TD415 system. Ever other systems we have tried has failed in one way or another. I won't say who's broke or how they broke so PLEASE don't ask. Each mfg has their own system for cleaning intervals and we may not follow their way. We have a way of cleaning and keeping records that suits our needs because of so much use.

- There is company that has an AR system that has some "parts don't need lubrication" and that failed before the end of the first day. I don't think some mfg's understand that people REALLY use their weapons and when you're rocking full-auto all day they NEED lubrication. My armorers and RSO's were laughing when it seized it up because we knew there was NO way it would last on our range.

- The parts that we see break more often are the bolt cam, bolt lugs shearing off, firing pins and gas keys shearing off the bolt carrier.

These are just a few of the things that I can think of on the top of my head. Please feel free to ask questions and I will try to respond sooner than later depending on my schedule.

V/R
Ron

ps: I am sure there are some grammatical errors as I tend to read the words into a sentence that are not there. Some sort of dyslexia-type of issue that plagued me through eight years of college.

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YMMV

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Really good info, there.

I imagine full-auto is an entirely different beast from semi-auto. Getting a gas tube cherry red on a regular basis has to create different problems than double-taps with the rare magazine dump, added in.

Keep it coming!

Bruce

My experience is with semi-auto use -- same with shooters around me. Civilian full auto use with any kind of volume will be at places like Battlefield Las Vegas.

I have seen bolt lugs break at around 10k rounds. Interestingly, the rifles still shot well and cycled fairly well with one broken lung. Most bolts will start showing wear at around 5k rounds. Most bolt lugs show some pretty ugly beveling at 10k rounds.

At one carbine course I attended an overseas contractor had major issues with his SBR, which had about 19k rounds going in. His mil-spec trigger failed on the second day -- which was pretty easy to fix, by dropping in a spare trigger. On day three his upper went to a single shot, and I was amazed how well he adapted to using the charging handle after every round fired. His gas block and gas tube failed together -- gas block split and gas tube eroded away at the connection to the gas block. That contractor said his bolt snapped a lug at 11k or 12k rounds. He said he would install a new bolt prior to going back to work. He's quite fortunate the failures occurred during a class.

For my rifles, I've replaced 3 sets of gas rings that were very loose and worn. Technically not broken, as the gun still cycled.

I've replaced 3 firing pin retaining pins. They were bent, and hard to install back into the bolt after cleaning. Technically not broken, but on close inspection after retiring the pins, I noticed very small stress fractures on the pins.

I've pulled 2 AR barrels that no longer met my expectations for accuracy. They still shot sorta OK out to 100 yards, but vertical dispersion at 300 yards became intolerable. The barrels weren't broken, but their accuracy was.

I think the important consideration is retiring parts prior to failure. Especially after seeing that contractor's gas block and gas tube fail, I install new ones with barrel changes. When pulling barrels I look at bolt lugs closely. If they show wear, a new bolt goes in with the new barrel.

Things I have actually had break unexpectedly (meaning maintenance failure on my part): bolt lugs, firing pin, bolt catch. Things I have replaced before they might break with visible signs things are not right: cam pin, firing pin retaining pin, gas rings.
Things I have replaced before failure due to measurements but not visible damage: BCG (guaged).
FWIW.
I now replace BCG's on serious guns on a regular basis, they are cheap.

I was an armorer in the CG, and taught small arms to sailors...

Like the guy above, locking lugs, gas key, gas tube...etc...

We usually used the same weapons at the range to save our other weapons for rotational spares, or if someone suffered a loss or break. So we had some. M16s with so many rounds thru them we had to swap out barrels because they would fail the throat gage.

But the strangest thing I saw was while coaching a new sailor, his front sight block literally started moving forward. The gun wouldn’t cycle right. Seems the tapered pins holding the FSB in had fallen out while he was qualifying. They were there just under the rifle...I picked em up, slid the FSB and gas tube back into the rifle, stuck the pins in and had him keep shooting. He qualified with duct tape and an Expert ribbon...when we were done for the day, I hammered the pins in place and never had another problem with that rifle.

I was a unit armorer for three years. Out of all the usual subjects it's the extractor spring and firing pin retaining pin that fail the most. The retaining pin is easy to damage, and once you bend it back and forth a few times it's prone to failure. The one part that used to be a problem was firing pins because back in the 1980's we were instructed to use the pin as a cleaning tool, causing excessive wear to the part. Once they stopped that practice the problem went away. The most surprising parts issue I found was trigger and hammer pins walking out under use. This was not caused by the egging out of the holes in the receiver, but by the worng part getting into the supply system. The hammer and trigger pins are supposed to have a groove that the trigger spring sits in, preventing the pin from walking. At some point in the mid 2000's, the Army ended up using a pin with no groove. It took me a while to identify all the affected rifles and get the parts replaced.

Now a word on 'hard' use. Unless you are running constant full auto, or are doing semi auto mag dumps to the point of needing a glove to touch the hand guards, you're not a 'hard' user. Suppressor use causes different issues, but they are generally well known. It's not the round count that's the abusive part, it's the heat. Excessive heat causes more firearms failures than just about any other factor.

Edited for spelling.

This message has been edited. Last edited by: SgtGold,

If you are just looking for oddball, Ive seen what i attribute to a bad round crater a firing pin and destroy a buffer to the point where there were parts of it all throughout the receiver area. Otherwise its just the normal springs, gas rings and bolt components. Crap QC and crap components aside of course.

I have been a police armorer for 20+ years.

My answer is simple: Anytime anyone tries out some new high speed part, it will screw up.

Other than mid length gas tubes on 16 inch barrels, Aimpoint sights and some free floated forearms, I cannot think of a single modification intended to improve performance which has not eventually ended in regret.

The base rifle is pretty reliable if you buy a decent quality one.

Most replaced parts are rings, barrels, and gas tubes in that order.

I am especially unimpressed with pistons, I am so glad that fad is over.

quote:

Originally posted by Sig209:
this question was put to them and one of their armorers posted this on another board.

This is a very informative thread, and especially that post.
(And more support for my not being impressed with piston guns either, although I do have an MCX because of its size.)

hopefully i don't get disciplined for cross-posting

the thread is here. keep in mind it started in 2015 so its long and some comments are dated a few years back. but it does offer a neat technical perspective from a high volume arms room with lots of Q and A

https://www.ar15.com/forums/AR...e/118-677135/?page=1

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quote:

Originally posted by Sig209:
the thread is here.

The information there is absolutely amazing!
Thank you. (Finished.)

Added:
Notable comments that I remember on the AR forum.

Previously mentioned: piston guns were more prone to parts breakage failures than DI.
Recommended lubes: Lucas oil (less “misting” that kept clients’ clothes cleaner) and in particular TW-25B (less misting and easier clean up).
EOTech sights were not nearly as durable as ACOGs and Aimpoints; the Aimpoint PRO was what was most commonly used and was very durable. The SIG Romeo seemed to be holding up well. A Docter sight pictured on one gun was surprisingly durable despite the rough treatment the guns received.
AR barrel length made a significant different on parts longevity. Bolt lug and hammer pin failures were much more common with SBRs.
Chrome lined barrels lasted about twice as long as Nitrided before bullets started keyholing (their high use guns were not fired at long distances, so they didn’t monitor precision any more closely than that).
Mossberg model 500 and Remington 870 slide action (pump action) shotguns had very short operating lives under their hard use conditions. The company found it less expensive to simply replace broken guns than repair them. The Benelli M4, however, kept going and going (albeit with somewhat less use). The company owner said that if he had to depend on one shotgun for critical purposes it would be the Benelli.
PSA receivers were surprisingly good, especially for the cost.
The company did not use steel cased ammunition; extractor failure rates were much higher.

Added added:
PMags are not as durable as metal mags (Brownells were mentioned as good).

This message has been edited. Last edited by: sigfreund,

I have broken:


The fastener holding the gas key to the carrier. (one failed, the other held, rifle kept functioning.)


Gas rings run to failure. (rifle kept functioning, but when I took it down to clean it the rings were clearly shot.)


broken firing pin retaining pin. (locked the rifle up completely, had to disassemble the stock/receiver extension to get it apart)


Haven't broken a bolt yet.

I replace most springs on regular intervals so I haven't had an extractor spring go on me.



The failure of the firing pin retaining pin rendered the rifle completely non-firing.

I have considered purchasing the solid tool-steel part available from Dillon Precision, to replace the generic cotter key pin. If a bolt breaks at the cam pin, the rifle will go down. But otherwise, even shearing a bolt lug, the rifle will keep running unless that lug winds up somewhere important.


I witnessed a primer ejected from within a case and make it's way into the cam pin slot of a bolt carrier.

That rifle was completely locked up as well.

Great 1st hand source info from Battlefield Vegas!