Colt AR-15 KABOOM

6920upperblownapart-tfb-tm

Parallel got the fright of his life when participating in a Magpul Dynamics “Dynamic Carbine” course.

Side of upper receiver blown open.
Bolt carrier split.
Bolt face split.

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.

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Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


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  • jdun1911

    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.

  • Lance

    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.

  • http://savage-doc.blogspot.com/ JDShaw

    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

  • jdun1911

    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.

  • jdun1911

    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.

  • Will

    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!

  • Keith Applegate

    “ammo used was factory XM193.”

    I wonder if he means, by any chance, Federal Black Box/Tan Box XM193?

  • CMathews

    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.

  • Lance

    I think the upper was a bad casting the ammo and barrel i think wert the reason it blew up.

  • Whatever

    There must have been something really energetic going on for the bolt carrier to end up split on the bottom like that.

  • jdun1911

    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.

  • jdun1911

    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.

  • W.E.G.

    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?

  • http://www.youtube.com/watch?v=h35JTL9yy-0&NR=1 Machine Gun Kelly

    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!

  • Jake

    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.

  • Keith Applegate

    “Pressure builds super fast. Faster than the bullet can move out of the way.”

    OW MY EYES!!!

    Oh come on now Jake, that is just so wrong on so many levels. Do you actually believe that? I hope not. If so then it’s painully obvious you know exactly nothing about the internal ballistics of the modern smokeless powder cartridge.

    There is no way you can achieve detonation with any currently available commercial smokeless gunpowder in a cartridge as small as the .44 Magnum or the .223 Remington.

    The only problem one might encounter as a result of dropping a 9mm powder charge into a .44 magnum case would be the bullet MIGHT lodge itself in the barrel somewhere short of the muzzle.

    In my career, I have examined well over a dozen kabooms and in every single instance (where there was not a previous obstruction in the bore), EVERY single one was caused by a LARGER than safe powder charge. As I understand it, so far, no one, anywhere, has ever been able to create a kaboom on purpose in any sort of small arms by simply reducing powder charges.

    And there are many who have tried to do so.

    Extensively tried to do so.

    Myself included.

    In 1983, using every then commercially available handgun propellant, I personally supervised testing of reduced powder charges in .380acp, 9mm Luger, Super .38, .38 Special, .357 Magnum, .41 Magnum, .44 Special, .44 Magnum, .45acp and .45 Colt. And I do mean EVERY commercial powder, as well as several non-cannister powders, suitable for handgun use available in the US, from the fastest burning to the slowest burning in EACH of the aforementioned calibers. Using several bullet weights in each caliber to boot. Now lemme tell you, that was a heck of a lot of testing.
    For each caliber/powder/bullet combination, I lowered the charge weight until the bullets would no longer reliably clear the barrel.
    Wanna guess what happened?
    Not a damned thing.
    There were absolutely NO indications of any sort of excess pressures.
    Without fail, as charge weights were lowered, velocities simply became slower. Until they became too slow to overcome the friction of the bore.

    Even with the dreaded H-110/WW296 (and 297) there were no kabooms. Not even close. All of the reloading manuals caution against using reduced charges of 110/296 (I use the term 110/296 because the two powders are exactly the same-from the from same formula on the machinery), beacuse there IS a problem with using reduced loadings of 110/296. That problem however is NOT detonation. What happens is that one shot will go off just fine while the very next just might leave you with a bullet stuck halfway down the bore. Now if one were so careless as to execute a double tap with one of those non-recommended reduced loadings one could very well have a problem. But then no one in their right mind chooses 110/296 for reduced loadings anyway right? After all it was designed for full-tilt-boogie power levels.

    So here we are, nearly a full decade into the 21st century and yet there are still untold numbers of Chairborne Rangers out there that insist on perpetuating these urbane myths about mystical exploding powder charges. And it’s all just so much yellow precipitation down our necks to shift focus away from careless handloading.

    Face the facts Jake, your IPSC buddy simply double charged a case and didn’t want to man up to the truth that it was 100% his fault.

  • Jake

    We pulled the other five bullets in the gun and several in the box and the charge was way less than the recommended load in all of them. The powder he was using would have over filled the case with a double charge.

    I’m referring to a low load density and to the powder charge shifting. The way the pressure curve gets erratic. I’m sure you can dig out some data from your testing. In a laboratory where you can measure the pressure, not read primers? I’ve also been reloading and shooting for over 30 years.

    Thanks for the insult, always the first thing out of the mouth of you “smarter than the rest of us” people.

    This has been talked about for years. I had even talked to Marty Liggins at Accurate Arms Powder about this very subject back in the 90′s. They were aware of it back then. A powder manufacturer. Hmm Nothing mythological about it my friend. But hey, I guess the rest of us are not as smart as you.

    I was just throwing in another possibility for the AR failure. As you are aware, ammunition companies are running mad to keep up with demand. Long hours and high speed can lead to issues with ammunition. Any ammunition.

    It’s explained here better in this one of many examples:

    Hoss Topper [email protected]
    wrote:

    About low charge detonation in firearms

    spread out along the bottom of the case with a lot of airspace left above
    it, it can — sometimes — detonate or at least burn MUCH more rapidly.

    In fact, it will burn too slowly at the beginning. Later on, the powder
    burns very fast.

    According to ammunition and powder companies, the mechanism is not yet fully understood.

    ( Wow even the companies that make the powder and ammunition don’t understand it. Call them Mr. Applegate and clear it all up!)

    Meanwhile, reloader’s are advised to use caution.

    How come? In think the mechanism isn’t that difficult at all to
    understand. If you have a too light load unevenly spread in the case,
    the charge will ignite partly, slowly or not at all because of too low
    a pressure, too weak a primer or uneven distribution of the flame
    across the powder volume. Then the bullet may start decelerating or
    even stops in the barrel.

    Should that happen, the gases behind the bullet stagnate and the
    pressure and temperature rise sharply at the bullet base. As the powder
    charge always moves with the bullet, the powder starts burning rapidly
    at the bullet base (local pressure peak) and amplifies the pressure
    peak. Next, the pressure peak will start traveling towards the bolt in
    the barrel and reflects back at the case bottom (bolt face). All the time,
    the pressure wave gains more and more energy from the powder spread
    along the case and the barrel behind the bullet. When this oscillation
    reaches high enough amplitude, it turns into a shockwave, i.e. a
    detonation (powder is still present to provide the shock wave with
    energy).

    [Mr. Applegate says this is a myth]

    Such a small charge detonation is always preceded by several pressure
    peaks (can be seen in a test barrel with pressure transducers) until
    the peaks reach very high pressures and all of the powder still left
    burns with a single pass of the wave, which indicates a real
    detonation.

    fast-burning pistol powders in squib loads for large-cased rifle calibers.

    Pistol powders (especially the porous types) ignite easier than coated
    rifle powders. In addition, it is best to use as strong a primer as
    available for those light loads to ensure proper ignition of the
    powder. Also, as pistol powders burn faster, the pressure rises high
    enough for stable burning and for keeping the bullet under acceleration
    until the powder burns out.

    Using pistol or other easily igniting and fast burning propellant is
    the correct procedure to avoid a low charge detonation. A filler also
    helps, as the powder charge is kept close to the primer and ignites all
    at once.

    BTW, revolvers are particularly prone to low charge detonation, as the
    bullet hits the lands hard and always decelerates strongly.

    [I think I described a revolver in my post. Imagine that.]

    • http://www.thefirearmblog.com Steve

      Jake, thanks for the info.

  • Jake

    Your welcome Steve. Great site you have here. Didn’t want to start a fire in here.

  • sniper1

    it was clearly a case head seperation

  • http://none BillyJoe

    I load 6.3 grains Unique behind 240 grain swaged lead semi-wadcutters for my Rossi M720, 3-inch barrel .44 Special. I press a wad made from polystyrene meat trays down into contact with the powder that fills the case about half-way up. It is a STOUT load for the gun that weighs about 30 ounces. Can you tell me if I’m eventually going to blow up the gun? Thanks for any input!

  • DeptArmorer

    Out of battery firing can be caused by foreign material on the bolt face striking the primer, but never results in a kaboom of this scale. Typically the gas vents out of the magazine as the design intends as the bolt is not locked. If it were locked, it would be a slam fire which doesn’t damage the weapon.

    This is a textbook example of case failure, caused by a hot load or excessive head space. The key in determining the cause requires analysis of the casing for evidence of a hot load. Usually the case goes slightly molten and will leave deep marks on the rim from the extractor.

    Were there several FTF on multiple rounds prior? That is an indication of excessive headspace.

    Contrary to what another comment said, headspace IS important with an AR. A barrel and bolt on the opposite sides of tolerance will go out of spec in a hurry. Even the removal and reinstallation of the same barrel can make a rifle out of spec due to changes in angel of the bolt relative to the barrel extention. There is only .0085″ of tolerance allowable in the 5.56mm chamber to be considered safe, so there really isn’t much room for error.