As pointed out by one person before, it is impossible for the firing pin to strike the primer unless the bolt carrier is fully forward.  A high primer can result in an out of battery.  And the bolt is till locked up, as manghu67 stated.

It is difficult to overcharge the 223 case except with a very few rifle poweders, OR pistol powder.

But very likely, it was an undercharge.  This is why many powders state do not reduce the loade below X amount.

AMOS posted "...we found they were undercharged. When the cartridge layed horizontal, the powder charge did not cover the flash hole at the primer pocket. When the primer shot fire into the shell case, it ignited all the powder at once, hence bringing the peak dwell pressure over the acceptable level."

I would place my bets on this one.

Ok... newbie chiming in here....

The pictures appear (to me anyway) to show that the bolt was forced back into an immoble carrier. The carrier appears to be split in the pics.  Also, the second to last pic seesm to show some of the locking "ears" sheared off.

Am I way off here or was the carrier somehow unable to cycle?

Feel free to correct/critisize as I am learning this stuff.

I saw this same exact thing happen back in '94, with the same results.  Weapon was properly head spaced and fired in excess of 600 rounds before kaboom.  General consensus was the reloaded ammo was the cause.  I'd checked with Dan Shea, at Long Mountain Oufitters, and he stated that an undercharged 5.56 round WILL detonate and cause the results we saw.

On a slightly different slant, while cross contamination of pistol powder is possible, the result would be the same as an undercharged case.  I suspect, burning a small amount of powder, in a rifle case designed for much more, will cause a short, high pressure curve.

HTH.

Deleted post. I refuse to respond to the "detonation" theory other than to say it is the BigFoot of reloading.

If it's real, tell me the load that will detonate.

Pete
(who has personally reloaded a hell of a lot of reduced load cartridges and never had one blow up yet.)

The bolt is already in the closed/locked possition (locked into the barrel extension so it cant move) when you fire.

The gas ports, go's though the front sight, down the gas tube, into the carrier key, into the bolt carrier, the pressure inside the carrier unlocks the bolt to the forward/unlocked possition and blows the carrier down the buffer tube.

In this case, one way or another, the gas pressure that ported into the carrier was way too high and split the carrier.

It was over or under loaded ammuntion.

The funny part to me is, everytime I have seen a KB the barrel never exploded. (if you have pictures of one please show me)

I guess they are just too tough, Anyone else want to give it a shot? [:D]

Hi Just Looking! In the over pressure failure that we examined, the barrel suffered no damage... It appeared to us, that the chamber pressure was so extreme that it caused the bolt to continue to rotate in the locking direction. One has to remember that the lugs on the bolt, lock it in a linear direction, not in rotation, this is controlled by the cam pin & carrier pin slot alone. As we know, the bolt carrier key will not let the carrier rotate in the upper receiver. The over-rotating bolt stresses the carrier via the cam pin, and the whole works fails just about the time the gas port comes open...  at this point, in our example, the bolt had actually over rotated to the next set of lugs, (not to many degrees of rotation if you look at how they are made!) and pushed rearward. Jamming the now fractured & unlockable bolt carrier to the rear, by forcing/gouging the cam pin back into the upper! The gas and metal comming down thru the mag well is just icing on the cake, as most or all, of the severe damage is has already transpired! I'm pretty sure this is what they will find on the example outlined in this thread... I don't believe the bolt carrier is subject to failure by gas pressure alone, I believe that under this circumstance, you would have an extremely fast & sharp recoil impulse, but no severe damage... at least, not the type of carnage discribed above.. all the above observations are just my opinions though, I don't want to twist any Tigers tails! Thanks, till...later....GT

I am no expert by no means, I have only been reloading since 1970. One of my first Speer Reloading Manuals stated "Do not try to use relaitively slow-burning powders in greatly reduced charges. There is some evidence of extreme pressure occuring under these circumstances." They also talk about using Kapok as a filler to keep the powder compressed against the primer. I never wanted to test their theroy or try to prove them wrong. I have used reduced loads in revolvers with fast burning powder. Loaded them just enough where the bullet would not get stuck in the barrel. Great load for paper targets at 25 yards in. Then in the late 80's we had an M-16 have a KB just like what happened here-judging from the pictures posted. The rifle was maintained by our Armorer and was checked on a regular basis along with the other M-16s. To save money, our department was using reloads at that time. Bullets were pulled and charges were weighed, several other rounds from the same lot of reloads were 1/3 to over 1/2 undercharged. We never tried to duplicate the KB. This DID happen. I wasn't privey to what type of powder the remanufactuer was using, or what recourse they took about the KB. Always remember that the OTC canister powder we use in the small cans has been tested and has to meet tight pressure curves for the loads published in data books. Making smokeless gun powder is an art, not an exact sceince-that is why powder which does not meet published canister spec data is sold to ammo manufactures and remaufactuers. They have the resources to build up a load using the out of spec powder. Not to say the powder is bad, it is out of spec to be used with the published data. My explanation for the KB may be completely wrong, however I believe overpressure was the cause. It may have been caused by fast burning pistol powder, incompatiable compressed rifle powder (I doubt this one), or over pressure from reduced charge of slow burning powder which a large cross section of the powder was ignited at one time which caused and immeditate spike of pressure that was more than the rifle could withstand. This is just my opinion from past experiences and observations, and it was never meant to piss people off.

Hey guys... While I was doing a little research on the net, not on this subject, I read a little article about Crimped Bullets and Kabooms... When I read that, I immediately thought of the exploding M4.

I was wondering if a crimped round could be a suspect???

Please clarify,
The the last round go BOOM as the bolt was feeding it, or did it BOOM after to squeezed the trigger and dropped the hammer???

There is something about that statement that does'nt sit right.

If that is the case, at x pressure the bullet would have left the casing and the result would have been a bullet exiting the muzzle at a much lower velocity as all the powder was consumed early in the bullet's travel along the bore. If if x pressure was achieved faster, the integral of the pressure/time is much lower.

There is something about that statement that does'nt sit right.

If that is the case, at x pressure the bullet would have left the casing and the result would have been a bullet exiting the muzzle at a much lower velocity as all the powder was consumed early in the bullet's travel along the bore. If if x pressure was achieved faster, the integral of the pressure/time is much lower


The findings of RCBS/SPEER, and others including Reloader magazines state the condition I described as causing the same over pressure as in hot load-wrong powder ect. The way it was described to me that when the powder is laying flat below the primer pocket all the way to the base of the bullet, the primer ignites the top level of the powder and burns down all at once. This not the way slow burning rifle powder was designed to work. It was designed to burn from one end to the other. ALL this powder igniting at once has now developed more pressure than a correct load of powder would have. This a reason there are different burning rates of powder and some work in some calibers and not well in others. You want a pretty full case of powder in a knecked down rifle cartridge. Way before you download and get to the dangerous level, your deviation will be off as your FPS will be way off. You need a pretty full case to get best accurcey, or use KAPOK filler (in bolt guns) semis must have correct pressure and dwell to make the action function and not beat up the rifle. Downloaded round with the powder below the primer pocket, primer ignites a large surface area of  powder at once causing chamber pressure to skyrocket over safe levels. The key here is that the pressure was over safe levels may have not been there long, but just long enough to transfer down the gas tube to the bolt. I don't plan on experimenting with reduced loads as I have read about the results from handloading manuals and articles-and have seen it first hand when we pulled the bullets of some other of the remanufactured rounds. It seems you can get away with reduced loads with fast burning powder in straight wall pistol cases. For the non believers, do a search or send a question about way reduced loads to a powder manufactuer.  AMOS

boomholzer:  turns out it was 2nd to last rnd that went boom, as i found one with a sizeable dent near the neck (where the front of the bolt carrier wouldve rammed it as the bottom spilt away) and carbon/powder burns on it...

the rifle fed and cycled fine up until that 2nd to last rnd... fed fine... squeezed trigger, dropped hammer, thats when all hell broke loose...

Amos- nobody can tell me an exact underloaded round that will detonate.

Don't you find this funny?

You would think that somebody could say "load 8 grains of H335 under a 62 grain bullet. Be sure the powder is in the case FLAT. It will detonate every time. Well, 3 out of 10 times. Well, actually we can't get it to detonate, but don't do it.

Let's all agree on this- we think it's overpressure from the ammunition, and nobody can tell exactly why. And we all agree ammuniton shouldn't do that!

i dont know jack squat about reloading, but i do know one thing: i agree with stinkypete... amunition should NOT do that!

i also know that itll be a cold day in hell before i feed ANY of my firearms ultramax again...

I really don't care if you believe me, but I am just going on what I have seen and read. There must be something to it, or they would not warn against it. I can't tell you, nor the experts can't either, how many ciggerettes you have to smoke before you get lung cancer, or how much absorption of certain chemicals through the skin will cause other types of cancer. In either case you should do it for health reasons. I really don't think the powder manufactuers sit around developing undercharged KB loads. They know it will happen. But if you have some time on your hands, why don't you loads some rounds down and prove me and the powder companies wrong? Even if it happens one out fifty rounds in underloads, isn't that enough, and say it happened? Just because I can't give you the exact load that causes a KB, doen't mean it doesn't happen, and I bet the remanufactuer doesn't know it either-as it is the last load they want to develop. In all I have read, NO ONE HAS EVER WROTE "Well actully we can't get it to detonate, but don't do that." I would like you to show me this statement in ANY reloading guide. "You would think someone could say load eight grains of HH335........." I think the researchers could give you a ball park on what it takes, but why would they publish this? Liability reasons-famous last words whatch this. There are idiots who would try to duplicate this condition. Stinkypete, my posting was stating what I have seen and read, and and was never meant to alter your thinking or your experiences. Let me know when you develop a KB load, or when you can prove the powder manufactuers wrong.  AMOS

On underloaded 223 ammo:

Before I knew better, I loaded and shot several hundred very light loads in a Mini-14 I had in the early 80's.  I wanted a squirrel load that wouldn't have much blast.

I got something about 1000fps with a 55 gr bullet.  Very accurate, and worked well on the little gray tree rats.  I also shot this a bunch on paper.

After reading all the warnings, I quit this loading, and threw away all my light loads.

I still shoot very light loads of bullseye in 38sp cases, though.

I never had a KB or signs of overpressure or detonation.  The only anomoly was lots of unburned powder grains and failure of the brass to seal to the chamber walls during firing.

This proves nothing, but I doubt the first undercharged round in a batch would have caused a KB, there would have more likely been a FTE due to low pressure on an earlier round were there more than one undercharged round in the lot.

I suspect wrong powder/overcharge.

I've read w/ interest all the comments in this thread.

[b]If as stated you were using Ultramax lead nosed 223 ammo[/b]

here's my quess at what happened.....

The lead nose caught on the non-M4 ramped edge of the upper and DROVE the lead nosed bullet back into the brass, then slipping up into the chamber into battery. Unfortunately the bullet was crammed back into to the case far enough to create a serious OVER-PRESSURE problem and hence you became a lucky survivor of an ammo related KABOOM.

Count your lucky stars, and [b]ALWAYS[/b] double check any ammo related hang-up of entry into battery of your AR or any semi-auto for that matter,  that "just don't feel right", as this can happen. I've seen even a Q3131A "crimped" round get driven back into the brass on more than one occassion.
Mike

mr_wilson:  rifle was running like a top... no misfeeds, no stutter during feeding... action was smooth and flawless until KB... when i say lead nose, we are talking like an 1/8" of lead at the very tip of the bullet... my dealer should be getting back with me in the next day or so regarding the cause...

You might want to hang on to some of that ammo yourself.  You may never be able to get any more of it and you might need it for later testing, legal issues, etc.

Yes consider your self lucky. I have been reloading for more than 20 years and have seen many major and minor KB's. Some of them have even happened to me. Thank goodness for safety glasses and ear muffs.

All of my reloading manuals have said and still say the same things. Over loaded ammo will result in high pressure. Compressed powder charges result in high pressures. Under loaded cartridges rifle cartridges cause pressure to react unpredictably, which to me means can go high or low. And different primers have differing effects on pressure.

And I think we all agree that this KB was a result of an OVER pressure condition. What caused it, we may never know, because there are so many factors involved, however the primary factor would be, in my humble opinion, the ammo.

Stinky Pete, a few years ago, CCI put out a warning about using their magnum primers on reduced charges. Because of their increased brillance, magnum primers ignited the reduced powder charge all at once instead of the controlled ignition caused by regular primers. This caused significant increases of chamber pressure. I will see if I can locate this warning and post it if found.

well, part of the verdict is back from dealer... right now he believes it is the ammo... case head failure... says there is a hole in the rear of the case... he wont know for sure until he recieves the ammo i sent him, which should be by friday... he checked headspacing, and it was dead on... primer was flat on extracted case, so it wasnt a high primer... he is sending me pictures... he said that the bolt is intact, but the extractor is bent out near the lug, which sounds like what is described in the documentation oldguy dug up from both armalite and bushmaster... sooooo, looks like potentially that this could fall back on the range or ammo mfg...  

Ballistics 101:
On the question of undercharged cases. I believe an undercharged can detonate if the conditions are right. The first thing one has to realize is that propellant burn rate is directly proportional (actually most of the time exponentially) to the surface area. You reloaders will notice that fast pistol ammunition is consideraly finer than rifle ammunition. Second thing to consider is that burn rate is also directly (once again exponential but for clarity sake) proportional to pressure.
If you have a charge that is lies below the centerline of the case then more of it (much larger surface area) will burn. This large surface will yield a large pressure which will yield a large burn rate which will yield a larger pressure which will yield a larger burn rate and so on until boom! Remember this all takes EXTREMELY fast. So given the free volume of a half filled case that will allow more propellant consumption before bullet release you get a very viloent reaction that can be considered a detonation, although it is more accurately called a self propagation.

aka anomalous propagation (hee hee remember that one).  you should know, you're the rocket scientist.  

good explanation....but it still went boom.

yeah that anomalous propagation blew up a lot more than al though, big boom!!! I do love that stuff, except when it is somebody's pride and joy and their life is at stake.

Okay guys and gals, check out this string for light loads in cartridges causing high chamber pressures.

[url]http://www.ar15.com/forums/topic.html?b=3&f=118&t=167637[/url]

and not in a good way!

that's weird..If I've seen photos of your AR, and your KB is amazingly similar to mine, only mine did much less damage to the rifle, not bulging upper or lower, however the carrier was split in the very same mode (refer to my post in troubleshooting section), have you any photo of the recovered brass?

I vote for the case head seperation/failure. Why the case head failed could be a few different reasons or a combination.[list]
[*]Powder[list=a][*]Wrong type - [blue]Unlikely or this would have happened before #90[/blue][/*]
[*]Overcharge - [blue]Possible[/blue][/*]
[*]Undercharge - [blue]Most likely[/blue][/*]
[*]Contamination - [blue]Possible, would check all prior cases for pressure signs.[/blue][/*]
[/list=a][/*]
[*]Brass[list=a][*]Excessive case length - execessive crimp and metal in throat area.[/*]
[*]Excessive sizing - case shoulder bumped back too far (headspace).[/*]
[*]weak case head - case may have been fired in an excessive headspaced gun on first fire causing brass to thin out in case head.[/*]
[*]Internal corrosion - once fired mil brass can sit for a long time before being processed.[/*][/list=a][/*]
[*]Damaged projectile base which casued an oversize condition. - [blue]Possible, but unlikely.[/blue][/*]
[*]Other Pucker factor[/*][/list]

An AR can fire out of battery from a high primer - but there would have been alot of brass shrapnel and the bolt would not be stuck in battery.

As for High pressure causing the carrier failure - remember the gas tube is only .025" wall thickness in the relieved areas where it goes through the weld spring & delta ring. It is much more likely that there would have been a catostropic gas tube failure before any damage to the carrier would occurr.

dealer stated that there is a hole near case head, which points to case head failure... he is sending me pics and the old rifle back once he has a chance to check out the ammo i sent him and render his final verdict... i will take more pics once i get it back...

Bump.

Just wondering what the final verdict was.  The case gave up the ghost or it detonated.

A hole in case head? Please take a look at my thread in this section, and tell me if your recovered case was similar to mine. You bolt carrier (as you would see comparing your photos to mines) splitted in a almost identical mode to mine. Also, when I checked what's happened at the range ad separated upper and lower, the bolt was stuck in the very same manner. I unlocked the bolt tapping it with a brass dowel and a plastic hammer, and lot of lubrificant. It seems that we had the very same kaboom, only that in mine the damage was less serious. Please if you can post picture of your recovered brass. thanks.

If the ammo you used was made by Ultramax they will stand behind it. You will need the box with the lot number on it. If you got "bulk" ammo you will be on your own. I would hope the range people will replace for you.

STS

I believe I would tend to believe this was from an undercharge rather than an overcharge. Even given the wrong powder it might be dificult to overcharge particullarly with a 55 gr bullet. The bullet to powder wt ratio would likely not be condusive to the type of pressure that is required to rupture the parts as you have shown. This assumes of course that there was not a potential flaw in the metal for some reason.

I believe that as Freeman and Profgab have pointed out this sounds more like an under charge that ignited a larger than normal surface area in the brass.

Another undercharge possibility is that potentially round 89 did not clear the barrel. Did you see it hit the target? It is possible to have a round cycle the bolt but not clear the barrel. If 89 was stuck in the barrel for some reason then round 90 on the back end would cause back pressure on the system and possibly cause a problem similar to what happened in you case.

DKreh

I was wondering what the outcome/solution of this incident was. I've been cruising the boards for quite a while (new to the boards not AR's-built my first back in the early 80's) and have revisited this thread quite a bit trying to keep up. Thanks!
iimagine [bounce]

I had that exact same thing happen to my OLY CAR97 after about 240 rounds. Scared the crap out of me. Oly tried to blame the ammo but two armorers claimed it was caused by firing out of battery or headspace problems. It was warrantied and now I have about 1500 rounds through it with no problems. [8D]

just marking this thread, I find it very informative.
I would love to know what really happened.  My .02 is ammo also.

still waiting for complete resolution, which i should have this comming week... we shall see...

Still checking in.....
iimagine

Is the verdict in about your carbine?  On pins and needles here.  I know some guys out here have your case in the back of their minds while building their own M-4's.  I know I do!  Just finished one.

DG

should have my old rifle and replacement parts back tomorrow, as promised by dealer...

Holding breath for ya,[:)]

that makes two of us...

now, should have some info tomorrow...

Just curious... What was the offical cause for the KABOOM???

Sorry to hear the news. Somebody posted a desire to buy broken parts for a display AR. Check the AR topic board for the past few days. Maybe you can recoop some of your loss on the upper.

You've got me on the edge of my seat, and my legs went numb about 2 days ago.

I realize that everyone wants to look at ammunition and that is probably the case here but no one has pointed toward the possibiltiy of excessive firing pin protrusion. This can cause the same result and I doubt the guy that put this thing together would admit to it when it is just as easy to blame the ammo. Peirce a primer on detonation once and see what kind of KB you get.

If it were excessive firing pin protrusion would it not have shown up as soon as he started firing?

not if the firing pin began to concave where it contacts the back of the bolt. I have had this happen and have been lucky enough to catch it before it caused any damage. I think that the reason you dont see this happen with M16 s is that the bolt carrier on the bottom isnt cut out by the firing pin and acts as a limit for the hammer. In august Olympic arms was at Camp Perry and the bolt carriers they are producing for ar15 s are enclosed like an M16.