Was just out shooting on a sunny Sunday today and had a serious failure with my M4A2.


I had fired about 150rds this morning, mostly bumpfiring, before it broke. My cousin picked it up and was shooting a 30rd he had just loaded and got about 20rds into it and ~ClicK~. He pulled back the charging handle and the front part with the lugs stayed (did not rotate out of the lugs) and the rear portion with the gas rings came back as normal. I fished out the front part with my Leatherman from the ejection port. There was a fired case in the chamber. Only ammo shot in it today was 62gr Barnaul FMJ which it seemed to like fine for the first 6-700 previous rds as do my other AR15's. The bolt had maybe 8-900 total rounds on it, just barely broke in actually. Lugs show little wear and gas rings are still fine, barely wore in.

 
   

 

The carrier, bolt pin, firing pin, extractor and ejector items all look fine. Just the bolt took a shit.

Also had my new Polytech folder out along with the SAR1, great time, zero malfs.

That's a reasonably common failure point, actually - seen a few others (if not exactly a bunch).

Get a new bolt, reassemble, and continue as before.

I don't see any markings on that bolt, (such as "MP C") to indicate that it's a name brand, properly-inspected bolt, so would you care to share the make of that bolt and how many rounds it had on it before failing?

Inspecting the bolt and other parts during routine disassembly for cleaning can give you a heads up whether the part will fail, as you can see where cracks are beginning many rounds before it'll fail like that one did.

It may be just a trick of the angles at which those pic were taken, but the bolt definitly looks "thinner" on one side of the cam pin hole on the other, so it may have been slightly out of spec to start with, and the thin side eventually failed, which then stressed the other side enough to fail as well.

seen a couple of bolt break like that, this is one reason I keep a spare bolt around.

The cam pin hole doesn't have enough radius.

Yes, a fairly common breakage point for an over accellerated Colt bolt.  We have done this several times with our sound suppressor on a GI 14.5" barrel, as this (sound suppressor)increases cyclic rate vs a non-suppresser 14.5" barrel.
So an anology here.  I notice in the picture that you have a 16-inch barrel.  So you bolt was seeing more thrust because of the extra time the gas has to work the carrier.  This probably exacerbated a weak design or material flaw in a "marginal" bolt designed for a much lower cyclic rate rifle (20-inch barrel).
I.e., this bolt may not have ever broke in a rifle format, and probably would have lasted a little longer than it did if you had had a 14.5-inch barrel.
This is yet another example indicating that forend rail systems like the RIS and RAS don't cause bolt failures.
ColdBlue sends...

Troy - certain others have made claims that the RIS/RAS has placed on undue load on the upper reciever etc.


postban
Is this a SGW - Oly Arms gun? Complete or?

The lower is clearly SGW (Oly), how about the rest of the gun, specifically the bolt?

This failure is more common with non-milspec parts (ie MA, Mod 1, etc.). The major malfunction with us about 5 per a 4 day class (of 200 students) is broken lugs. Although not uncommon, that is why the new bolts are marked manufacturer codes, ie (MPAC, FNDC, instead of the old MPC and FNC). This new system really aids in isolating bad batches of spare parts. Go figure the civilian sector is full of the FNC and MPC parts.  
Thanks
V

raises hand.

you put a lot of stress on a non mil-spec bolt simulating FA fire on a semi by bumping, i've had that happen on an armalite. no defects, it's just a lot of abuse.
it happens.
(edited to add, sweet lookin' 'bine)

In every instance i have heard of a bolt breaking like this, dating back to the old AR15-Lists, it was an Olympic arms rifle.

What brand is yours?

Alternative rail forend designers that secure to the full length of the upper receiver rail to obtain adequate purchase to the host weapon.  These designs generally allow for the barrel to be free floating, as opposed to our M4 and M5 RAS (and the Carbine RIS) that partially attach to the barrel.
It turned out to be a good marketing story, as it has taken on the status of an "urban myth".
ColdBlue sends...

Only broken bolt I've ever seen in 36 years shooting this system was, I believe, a DPMS bolt in an AR15.  My units have fired millions of rounds with no broken bolts.  I can't believe I'm just [i]lucky[/i].

-- Chuck

Lower is stop sign oly but all the guts/parts are Model 1 Sales. Bolt has no markings, MP, MPC or otherwise.

Thanks for the replies guys.

I had 3 bolts fail like that. 2 of them only broke on one side, the other one broke completly through on one side and 3/4 of the way through on the other. It also broke 3/4 way around the tail of the bolt behind the gas rings. All 3 were on the same gun, a Nesard 16" shorty. Each bolt only lasted 500 rounds or less. All bolts passed hardness testing and it was determined that all failures were due to an oversize gas port. The barrel was replaced and all was well for 3000+ rounds. Gauge your gas port opening.

I honestly have never experienced this.  I have several hundred k of 5.56 down range and seen millions more.

I guess it a lesson learned to stick to quality manufacturers.

I have seen this happen with both Oly arms and Professional Ordinance bolts.  

I think...  Isn't the carbon fiber AR pistol made by Professional Ordinance?  I seem to always forget the name, but it was that company.

I've got about half dozen or so (Colt mfr. MPC marked)here at work they have broken in various modes of fire: semi, bursting and F.A.

One fella I work with had two break first one broke then fixed and he put in a factory replacement and  it broke in 30 rounds.

It's happens for the most part only in the M4 series. Plus cam pins break from time to time also. I had an oirdnance engineer tell me they are working on a fix (newer materials).....we'll see what happens

I have seen this happen on Colt, Bushmaster and Olympic, probably even a few others that I cannot remember.

It seems tohappen more often for FA, short barrels, with suppressors, etc.

I do not consider this unusual, just not common.

If you have not seen this, then you need to shoot some more! :-)

If you'ld of had a PRI Fatboy tube this never would have happened.


(I hate it when you guys bring up AK's < they are crap and always will be. and I own 2 AK's and 9 AR-15's so I'm not totally full of shit. It has never been proven that AK's are more reliable (actually the opposite in Army trials).

When you go to an AK you get arcaic magazine loading (no bolt hold-open, and the camming mag load), lose the nice sights , lose some accuracy, gain weight, lose some controllability and for what?  Because of an early Vietnam War scare story and a no-longer existant problem.


Ar-15's are Damn near scientific if you do your homework and use the right part this kind of thing will never happen.

I managed to split one several years back.  It was a factory Oly Arms with only a few thousand rounds through it.

Ranger Sales stands by what it sells. Took it to a show where they were set up today. Showed the guy I bought it from and he swapped it with a new bolt no charge. I was so happy I bought another one for a spare. He kept the busted one to "send back for credit".

Thanks Ranger

I have been trying to find a photo of these for weeks. Anyone have one, or a link to one?



The AK design's reliabilty isn't a myth. Vietnam era specops/specwar were known to use them on long-range recons because of this.



Sad truth is, the AR's design (sans gas piston & tighter tolerances) makes it more finnicky. By contrast, the AK's looser design tolerances & use of a gas piston owe it a more "forgiving" nature. But in the end, the difference in reliability between them is often overexaggerated, particularly because the AR's improvements have addressed the issue - chrome lining (J. Sullivan himself has said that the omission of chrome lining was, "...downright stupid."), re-calibrating the buffer design to slow the cyclic rate, modifying some of the extraction components, etc., etc. The newer aftermarket stuff (PRI fatboy tube among them) increases the reliability factor still further.

The AR's ill-repute in 'Nam is attributable to its rushed delivery into service, bypassing R&D & T&E that would've produced a better performing final product. The final product is more akin to what we have now than it was to the original E1.