Colt AR-15 KABOOM
Parallel got the fright of his life when participating in a Magpul Dynamics "Dynamic Carbine" course.
The drill was firing from the urban prone, weapon side position. We loaded and made ready and I waited for the threat command. When the threat command came I went into the urban prone position and fired. On the second round the upper receiver blew apart. It took a few seconds for me to get oriented and realize what had just happened. I checked to see that there wasn’t another round in the chamber and raised my hand to let Travis know there was a problem. Travis was already on the way as he said that he thought that I was on fire from all of the smoke that was rising from me. There was a medic who checked me out real good to ensure that some shrapnel hadn’t penetrated my skin anywhere without my being aware of it. I sustained only minor injuries (a bruise on the left forearm and some flash burn to the face).
...
The 6920 is on its way to Colt Manufacturing for analysis as of this posting. I will certainly post the results of the analysis as well as the resolution when that information is available. I would appreciate it if the wild guesses as to the cause of this failure were withheld until Colt Manufacturing has had a chance to check it out. I will give a few facts that will help to keep the conjecture to a minimum. The barrel was clear before and after the event and the ammo used was factory XM193. I don't know if the brass was ejected, it appeared to be, however, there could have been part of the brass case left in the chamber, I was too busy trying to get back to training to check, then the gun went via FEDEX to Colt before I had the chance to check because I was trying to catch up on all of the work I had neglected while out running and gunning.
Many thanks to jdun1911 for emailing me the info.
It is almost impossible for an AR to fire out of battery. You can rule out out of battery. 99.9999999% KB! IMO are ammo related.
YEOW!!!! It must have been a bad casting in the Colt factory. While I say it happens to every mas produced gun. I think “Parelle” should get a free AR-15 carbine from colt. Colts a good name and I think when one of there products fails they need to step up.
The list of suspects (presuming a clear barrel and otherwise operations under normal conditions) is fairly short.
1. Bad headspace; chamber pressure spike
2. Bad cartridge load: chamber pressure spike
3. Out of spec chamber and bolt: normal pressure but catastrophic failure
Headspace isn’t a problem in AR15. Headspace are done at the barrel manufacture level. Hence you can swap bolts without the need to check for headspace. It either work or it doesn’t
AR15 bad bolt are always associated with the locking lugs or cam pin breaking in few hundred rounds.
Out of spec chamber is associated with failure to feed.
For those that are wondering why the AR15 can’t fire out of battery.
Take your BCG out.
Compress the bolt (locked position, in battery).
Depress the firepin from the back.
You will notice that fire pin is sticking out of the fire pin hole.
Extend the bolt (forward, this is the unlock position, out of battery).
Depress the firepin from the back.
You will notice the fire pin isn’t sticking out of the fire pin hole. If the fire pin can’t strike the primer that means the round won’t go off.
I find it curious that the dust cover and mounting pin is warped so much that it will not swing open far enough to lay against the receiver, where it sits after the bolt assembly cycles the first time. This would seem to indicate that the failure occurred from firing the first round, not the second. It’s possible that the cover was damaged prior to this incident, but the bulged cover is consistent with an internal explosion while closed, and would be unlikely to occur otherwise.
It is possible that the gun was being held close enough to an object to keep the cover from swinging fully open, but then that raises the question of where did the first empty go?
From the looks of it, I would say that that failure mode would be safer for a left hander!
“ammo used was factory XM193.”
I wonder if he means, by any chance, Federal Black Box/Tan Box XM193?
I’m just glad you didn’t incur any major injuries. Hope that Colt is swift with their investigation so you can get back on the range.
I think the upper was a bad casting the ammo and barrel i think wert the reason it blew up.
There must have been something really energetic going on for the bolt carrier to end up split on the bottom like that.
Colt doesn’t cast their upper. Colts upper and lower are made from forge 7075-T6.
There are no cast upper or lower in the market today IIRC. There were before 2000 but not anymore. All upper and lower are either made with Billet (6065-T6) or Forge (7075-T6). Of the two the forge is stronger and it is what the vast majority of AR15 receivers are made off.
Keith Applegate,
Yes that is what he meant. There have been reports of problems with the XM193 for sometime.
http://www.thegunzone.com/stag15_lc.html
Here is another AR15 that got blown up by XM193 ammo.
http://www.ar15.com/forums/topic.html?b=3&f=16&t=440162
Always wear safety glass when shooting.
Here was another AR15 KB! posted on M4carbin almost two years ago.
Someone was arguing that the AR was able to fire out of battery. Nate cut his bolt out and took pictures to show it can’t. The bolt must be fully close in order for the firepin to reach the primer.
http://www.m4carbine.net/showthread.php?t=30053&page=5
As with the other two cases the AR was feeding XM193.
Here’s an idea.
Shooter lying on his right side.
Ejection port facing toward ground.
Ejection port very close to ground.
Ground has small bits of rock.
First shot causes bit of rock to enter ejection port.
Bit of rock lodges between boltface and primer of second round.
Bolt comes into almost-battery with rock still lodged against primer.
Trigger pulled.
Hammer strikes rear of firing pin.
Firing pin cannot reach primer because of out-of-battery status of bolt.
Force of hammer striking firing pin drives bolt/carrier assembly against rock.
Rock is in contact with primer.
Bolt is out of battery.
Primer fires.
Round discharges out of battery.
Possible?
WOW! What more can you say, good damn thing your alright!
You should have just bought yourself a new upper.
Colt is never going to admit to wrong doing, Colt will come to the conclusion it was the ammo or etc, etc, etc.
If their at fault you get a free upper and they will push the blame as above, so either way you’ll get a new gun.
Just my 2 cents worth!
There is one other possibility. It looks to me as as if the BCG just backed up due to excessive pressure. It is very hard to double charge a .223/5.56 case, but it is very possible to ’short’ charge one. A friend of mine totaled a S&W 629 this way. He shot with me a lot. We were shooting IPSC at the time and doing a bunch of reloading. He failed to set his powder measure to the correct load. He had his mind on 9mm and the load was about half of what the .44 load was. The other 5 rounds in the revolver were half of what they should have been when pulled later. It blew the top of the cylinder and top strap off the revolver. How? On a filled cartridge the powder burns kind of like a fuse only real fast from back to front. Pressure builds slowly. On a short charged round the powder burns along the top and down. Pressure builds super fast. Faster than the bullet can move out of the way. The bullet will exit, but the gun will fail also. I saw a Glock 10mm go up like this. I helped the owner pull 800 rounds and we found one other cartridge with a half charge. These were factory reloads he bought. Where the pressure from a normal round is a curve, this type of load would be a spike.