I blew up my AR!!!!!!!!!!!!!!

[Clayfish]

I don't think that it would be possible for a stress crack in the lower to cause a kaboom like the one you are describing. Just as stated above the upper reciver and barell take all of the pressure of the round being fired. I believe it was a broken cam pin. When you say you load one at a time do you fire one locking the mag back then load one in the chamber and hit the bolt release letting the bolt slam into the chambered round? Doing this over and over would cause the pin to break under the stress. The best way to load one at a time is load the mag and let the bolt feed the round from the mag.

[P-990]

I can't offer any theories, so I won't, but I do have a couple of observations.

1) I doubt that a stress-crack in the lower caused a KABOOM! As has been said, the AR locks up completely on the upper. Actually, the barrel, barrel extension and bolt all take the brunt of the force of firing. The Upper and lower just kind of hold all the parts together so they work.

2) I doubt that it was continuous single loading placing abnormal strain on parts. Highpower shooters shoot their ARs as single-shots probably 70-80% of the time, and I don't hear them talking about having abnormal rates of cam pin failures.

And for the record, I have seen a case come out of one AR-15 that looked as though it somehow fired out of battery. Primer popped out, case head bulged, blackened and torn up. The shooter never realized he had had a problem and finished the magazine without a hitch. That rifle is STILL shooting, 11 years later.

Just glad you or somebody else didn't get hurt!

[GeorgeF]

Well this begs the question - who's your insurance company? Thats pretty decent policy. Is it just for firearms or is it part of the household insurance?

[fhp490]

can you take a picture of the parts

[Cal 50]

Any cracks in the lower receiver could never lead to a blow up as described.
The entire lock up system is contained in the upper receiver. Was the cam pin noted as being sheared off under the flat part. That would surely cause the rifle to be able to go off without the bolt being properly rotated into battery.
If the rifle didn't fire immediatly upon going into battery it could not be caused by a high primer. A case head separation also could cause this kind of damage. Was the case head intact. Were there any telltale signs of high pressure noted on the case head. ie: case expanded at the web,shiny spot caused by the case flowing back into the ejector opening,cratered primer,etc.

I believe that I would also find a more qualified GUNSMITH that knows more about an AR type rifle that that gunsmith. His observations are a bit on the shakey side.

[DnPRK]

Agreed. That gunsmith does not know what he talking about if he says a crack in the lower caused the bolt to fail to lock in the barrel extension.

[PDshooter]

Please take a picture !

[44 AMP]

Symptoms described indicate firing out of battery. Cam pin seems the most likely reason. Good pictures would help a lot. Powder residue and burns have nothing to due with the lower reciever. Perhaps you were mistaken? Your gunsmith might be showing you the cracks in the lower as a problem, but they are not what caused a failure in the chamber area. If he says lower reciever cracks are why your gun went ka-boom, he is wrong.

A catastrophic failure of the lower reciever could result in the gun falling apart, or the bolt carrier flying out the back if the buffer suddenly "went away". There is no way it could have an effect at the chamber.

Why your gun fired out of battery, is still a cause for speculation, especially if it happened exactly as you describe. If you are certain there could be no error in the ammo, and that the rifle did not fire on closing, then it is most perplexing.

Detail photos of the interior parts would be of tremendous help in determining exactly what happened.

[Powderman]

First, there is NO way that any damage to the lower receiver would cause your rifle to blow. As an earlier poster mentioned, the entire firing cycle is contained in the upper receiver. The only thing the lower does is to hold the hammer, trigger, disconnector, pistol grip, stock and buffer into a cohesive unit. You can fire an AR15/M16 with the upper and lower completely separated--I would not recommend it though, because the bolt carrier group will come roaring out of the back of the upper at a high rate of speed. (Don't ask me how I know.... )

At any rate, what another poster mentioned seems to be the likely case.

First of all, how do you single load?

If you load from a magazine or SLED, the culprit is definitely overpressure--caused from the act of chambering the round pushing the bullet deeper in the case, and causing excess pressure.

While at the range, I was firing my AR when I noticed the bolt locking up about halfway through the extraction phase. I got it open, and noted that the extracted case was almost welded (!) to the bolt face. It literally looked like a .223 belted magnum case--the case web had swelled and swaged out.

Before that, I had an instance where a round had hung up upon chambering. Upon extraction of that round, I noted that the bullet had been jammed back into the case completely. I failed to heed that warning sign.

The cure for the overpressure round is to ensure that you crimp each and every round that is to be fired in a semiautomatic firearm.

For this, I highly recommend the Lee Factory Crimp die. Case neck length (while still important) is not critical; the die will apply the same crimp, over and over again. I have heard tales where this die will affect the accuracy of the loaded round--I have not found this to be the case.

Get the crimp die, chalk this one up to experience, and shoot well!

(And send your "gunsmith" friend back to school. )

[Daniel BOON]

I just quit reloading for my ar bushmaster; its tedious, and accuracy isn't any better than with factory ammo. I think I'll save my once fired brass, and trade it off for factory loaded.

[Sarge]

I just read this whole thread, and then scanned over it again- and I still don't know which particular 'premium' winchester powder you were loading. 748? 760? Forgive me if I missed it.

I have seen 2 AR's and one FAL let go in the manner you describe, and all three were at LE range quals. In all three cases the individual shooters had supplied their own ammo. Both the AR's were with small-outfit commercial reloads, and the FAL blew with Radway milsurp. In each case it was a blown casehead, which signifies excessive headspace, off-the-scale presure, or 'bad' brass- meaning weak in the casehead, due to excessive reloading, or manufacturing gremlins. I did read that you had loaded it only once, so I got that.

Bullet setback can cause exactly the pressure spike necessary to blow a gun- and despite your rather lengthy checklist, I did not see where you crimped the bullets at the end of the loading process. I'll vote with those who nixed the idea that a cracked lower would result in a blown upper. The lower has nothing to do with the lockup of the bolt lugs to the barrel.

No Sir, you had a pressure problem here and my vote goes to bullet setback, due to lack of a crimp. There is a good reason why military bullets have cannelures in them, and why military loads have the bullets essentially laquered into the case. My suggestion is that you skip the step of each completed cartridge will being "weighed to again ensure uniformity"- and get yourself a Lee Factory Crimp Die, to apply liberally in its place.

Sorry about your rifle, and I'm not trying to be a wiseass. I have been standing within 5 feet of three rifles that 'let go' and it is an attention getter. There are ways to prevent them, and it sound like you had gone to great lengths to do just that. Adding a firm crimp is the one thing I didn't see, and IMO the one thing that got you.

Good luck with your future reloading efforts.

[DWK1703]

The instance that started this thread is very possibly the result of a cam pin failure. Cam pin failures can occur, resulting in out-of-battery firings. I have personally seen four such catastrophic failures in both M16s and M4s, and have heard of at least a dozen others in military service, some of which involved nearly new weapons. The outcome is usually a fully separated case, with the front half left in the chamber, but not always. Sometimes the case is just blown out at the base, but not completely separated. Typically, there is no damage to the bolt lugs. The cam pin is separated completely at the firing pin hole, and the gas key on the bolt carrier is bent upward several degrees from impact of the cam pin head moving vertically. There is never damage to the firing pin, but there may be some damage to the cam pin slot in the bolt carrier. The cam pin hole at the top of the bolt is usually enlarged. The extractor claw may or may not be broken off. In most cases, the shooter reports that he (and in two cases, she) actually pulled the trigger before the "KaBoom" and there was no evidence of a "Slamfire." In two of the incidentss I was able to measure the chamber throat diameter, which was within specs. In no case am I aware of any injury to the shooter.

I personally did a test firing of a junk M16 without a cam pin in place, and the results were exactly as reported above. This is strong evidence that the cam pin can fail. I have no idea as to the possible cause(s) of such failures, however. I have personally examined, under high magnification, hundreds of used cam pins without finding evidence of fracture. However, a significant percentage (20-30%) of the cam pins examined showed severe pitting, especially around the firing pin hole. Having thought about this a great deal, I can conclude only that such incidents cannot be attributed to anything other than cam pin failure.

If anyone can shed more light on this phenomenon, I'm sure many would like to know.

[James K]

So we have two intelligent, well informed people who have witnessed similar failures. One says categorically, absolutely, that it is due to deep seated bullets. The other says categorically, absolutely, that it is due to cam pin failure.

As I have said, I believe that the latter was the cause of the failure, since high pressure alone won't act the way described. But it is interesting that the same report can produce such widely different analyses.

Jim

[Sarge]

So we have two intelligent, well informed people who have witnessed similar failures. One says categorically, absolutely, that it is due to deep seated bullets. The other says categorically, absolutely, that it is due to cam pin failure.

As I have said, I believe that the latter was the cause of the failure, since high pressure alone won't act the way described. But it is interesting that the same report can produce such widely different analyses.

Jim
__________________
Jim Keenan

I said it was a pressure problem, Jim- and my 'vote' went for deep-seated bullets. I think your classifying that as my saying it was "categorically, absolutely, that it is due to deep seated bullets" is a little beyond that.

I am basing the pressure diagnosis on the fact that the bullet made it halfway down the pipe... pressure obviously spiked catastrophically early in it's travels (travails?) and the brass couldn't contain it anymore. It had produced a good head of steam to wreak all that havoc, at the point that it did fail.

Based on the author's omission of any crimping operation, in his very detailed description of his loading process, I will go on paper as calling "setback" the most likely cause. I won't pretend that I could conclusively diagnose it if I had the remains in front of me- although I'd really like to see it. Especially the remains if the case head...if the primer pocket was enlarged or blown, and/or the headstamp 'blurred' by contact with the boltface- pressure just about has to be the culprit.

I will add however that I am still learning something new every day- and today is certainly no different.

Take care- and thank you for the compliment.

[James K]

My apology for the attempt at humor by using the terms "categorically" and "absolutely."

I agree that no one will know until the poster either provides more info and pictures, or until someone with more knowledge looks at the rifle. The fact is that few gunsmiths have ever seen a catastrophic failure (a tribute, I guess, to modern arms makers) and have no idea how to analyze one.

I accept that under some circumstances high pressure can result from bullet setback, even though my own experiments show that the pressure rise is nowhere near as great as sometimes claimed. It could be high enough to enlarge a primer pocket or blur a headstamp, but I don't think it would dissolve a case head as high pressure could in, say, an M1903. The AR-15 is pretty well protected against that kind of disaster.

Of course, the bolt lugs could shear under extremely high pressure, but I just don't think bullet setback could generate the hundreds of thousands of pounds needed to do that! Also, I think the poster would have mentioned it if the bolt lugs were gone.

My vote is still with a broken cam pin. That is not ruled out by the bullet having moved down the barrel. Even if the bolt head were not locked, the inertia of the bolt alone would retain enough pressure to move the bullet.

Jim

[Sarge]

You may well be correct Mr. Keenan, and I figured you were yanking my chain a little No problem.

On 1903's...I had a low-numbered sporterized Springfield back when I was 16, and dinosaurs roamed the earth. I was long on P&V and short on caution in those days, and utterly ignorant of the problems inherent in that batch. A buddy had a loader and we ran quite a number of stout reloads through that old gun. Mine must have been made on a day when the light was just right, because it stood the strain of a couple of teenagers with a loading press.

I also agree regarding the improved safety margins built into modern arms. Out of the three blown rifles I mentioned, no one was significantly injured. That alone says a lot.

I remain interested in hearing further expert diagnosis of the problem with the subject gun.

[Harry Bonar]

Dear Sir:
I know of no quality made firearm that "blows-up" with-out some human intervention! If the cartridges were "handloaded" then I think there is the problem.
Harry B.

[DWK1703]

One can blame these incidents on ammunition, but such does not stand up under scrutiny. First, the M16 (military version) can easily withstand chamber pressures well in excess of 80KPSI without damage (when fired with the bolt head lugs in place). I have information directly from Colt to this effect. They got such pressures by the use of pistol-type propellants, as it is absolutely impossible to force enough of the types of propellants normally used in the 5.56mm into the case to reach such chamber pressures. If you wish, pull the bullet on a round and see the propellant level for yourself. The sase is nearly full. Second, I have yet to see an incident of this nature in which either the lugs on the bolt or in the barrel extension were damaged - a certain indication of an out-of-battery firing condition. Also, in every case, the cam pin was fractured and separated at the thin section at the firing pin hole. I consider the cam pin design to be suspect at best, because the metal cross-sectional area at this point is only 0.027 square inches, about 1/3rd that of the pin body itself. I've often thought that a beefier cam pin or a smaller firing pin hole in the cam pin would be better.

I wish I had all the answers, but I don't. Probably having seen more of these incidents than anyone else in this thread, or maybe everyone combined, I know the symptoms well. However, I can't explain the reasons for the probable cam pin failures I have witnessed.

By the way - I failed to mention in my earlier posting that there was clearly a firing pin indentation in the primer in every case I know of, and that supports the lnvolved firers' stories that they actually pulled the trigger before the incident occurred. Let's keep this thread going, maybe someone has the answer.