View Full Version : Round "cooking off" in the magazine?
ryder021970
07-31-18, 19:55
A few weekends ago I was at the local range and some guys were in the other bay shooting AR's. One of them came up to the line and started firing.
As he squeezed off a round, his magazine floorplate was blown out and the remaining rounds, follower and spring was dumped out. the RO immediately commanded him to stop and they went through the clearing process etc.
It was though that a round cooked off in the magazine; others thought something sharp probably hit the primer, setting off the round.
No injury to anyone and the magazine was re-assembled without any apparent damage.
What do you think happened?
vicious_cb
07-31-18, 20:00
Kabooms will follow the path of least resistance which is down the magwell and out the bottom of the magazine. Sounds like a normal kaboom to me, nothing special.
Also setting off a round outside the chamber is pretty unimpressive, its just a big firecracker.
cctroupe11
07-31-18, 20:01
Sounds more like the weapon fired out of battery.
Cb and Troupe are on point.
It appears to me that he didn't reassemble his magazine properly and firing the weapon launched the floor plate. If a round went off while in the magazine there would be damage, at least to the magazine, possibly the lower as well. Of course a round being ignited without a chamber doesn't generate any real velocity. Or it did fire out of battery? In the two cases over the years of seeing this there was evidence of it happening.
ryder021970
07-31-18, 20:20
Thanks for the inputs, guys.
If it fired out of battery, would the bolt carrier still be able to extract and eject the shell casing? Unfortunately, I didn't see if it did.
I saw the magazine; I didn't see any damage to it so it.
Sounds more like the weapon fired out of battery.
How does an AR fire out of battery?
Rifleman_04
08-02-18, 08:29
How does an AR fire out of battery?
It didn’t.
The AR can not fire out of battery.
cctroupe11
08-02-18, 08:59
It didn’t.
The AR can not fire out of battery.
If the bolt is out of spec or the headspace is improperly set, an OOB detonation is completely possible resulting in a case head separation, blowing out the magazine and (sometimes) destroying the upper reciever. I have seen it happen.
Something similar happened to me with Canadian milsurp rounds. Round fired in battery. Way over pressure. Blew the bottom of the bolt carrier down through the magazine with all the rounds, spring, follower, floorplate, etc. The top of the bolt carrier had a longitudinal crack so that the key for the gas tube and the bolts just fell out when I finally got the upper apart. The upper receiver bowed out at the ejection port and bent the dust cover and rod.
Needless to say but that pretty much ended the day.
It didn’t.
The AR can not fire out of battery.
Thanks for squashing that. I hate that myth.
Sounds like a small kaboom... that could easily appear to be a mag cook off to an RO. They don't get that job for being the sharpest tool in the shed.
Did the shooter and RO find the round fired just before the alleged cook off? Probably just a typical blown case.
As for an OOB firing, isn't it impossible for the firing pin to protrude far enough to reach the primer until the bolt is locked?
If the bolt is out of spec or the headspace is improperly set, an OOB detonation is completely possible resulting in a case head separation, blowing out the magazine and (sometimes) destroying the upper reciever. I have seen it happen.
The firing pin doesn't protrude enough from the bolt face until the bolt locks into battery to ignite a primer.
Rifleman_04
08-02-18, 14:21
If the bolt is out of spec or the headspace is improperly set, an OOB detonation is completely possible resulting in a case head separation, blowing out the magazine and (sometimes) destroying the upper reciever. I have seen it happen.
No. Not with the AR/M16 FoW. Not possible.
What you sawr was a ruptured case head. Happens a lot with worn brass and crappy reloads.
Thanks for the con-ed, guys. I’ve heard of OOB’s in this weapon type but never saw one in person. Makes sense that OOB would be highly unlikely in this platform.
Rifleman_04
08-02-18, 16:26
The firing pin doesn't protrude enough from the bolt face until the bolt locks into battery to ignite a primer.
Also the hammer can’t make contact with the head of the firing pin when it’s out of battery.
My comment was a bait cast.. thanks for making my point without me having to be a dick..
serious amount of lead down range in short order to get to cook off territory. I wouldn't think that a cook off from an M-16 type weapon would be all that bad because
1. It's a closed bolt weapon and
2. It's not belt fed. (far less chance of run away if you have a malfunction you can't clear) Just take the mag out keep the weapon pointed in a safe direction. For us, we wait 3-5 seconds but only have 10 to clear it.
Not a cook off in the chamber...but...in the mag. Or set off by a sharp pointy thing in the mag. It's pretty unanimous that it was a blown case.
ryder021970
08-02-18, 19:39
So I was able to track down the fellow who had this incident. He said that the round in the chamber didn't cook off; one of the rounds in the mag went off. He said that shell casing has a gash about 1/8 inch long perpendicular to the extraction groove. He said it was a reloaded round.
It looks like they've reloaded that shell one too many times.
Was there an indentation on the primer? If the case was unsupported and went off it seems that rupture would be larger than an 1/8". How did he describe the spent case in the chamber, was it normal?
So I was able to track down the fellow who had this incident. He said that the round in the chamber didn't cook off; one of the rounds in the mag went off. He said that shell casing has a gash about 1/8 inch long perpendicular to the extraction groove. He said it was a reloaded round.
It looks like they've reloaded that shell one too many times.So it just decided "I'm worn out and wounded... Think I'll blow up"?
Something had to set it off. As in hitting the primer. People tumble live mil surp ammo in concrete mixers... (I don't, but some do)
So I was able to track down the fellow who had this incident. He said that the round in the chamber didn't cook off; one of the rounds in the mag went off. He said that shell casing has a gash about 1/8 inch long perpendicular to the extraction groove. He said it was a reloaded round.
It looks like they've reloaded that shell one too many times.
Are you saying a round in the mag fired while in the magazine?
I really dont think that happened- or did I misunderstand? How would it have an extraction groove?
He had a ruptured case and the gas blew out the mag. That's how it's supposed to work.
ryder021970
08-03-18, 02:57
Was there an indentation on the primer? If the case was unsupported and went off it seems that rupture would be larger than an 1/8". How did he describe the spent case in the chamber, was it normal?
Both shooter and RO said that as the bolt closed on the round, this "explosion" happened. Everything blew out through the floorplate. The round in the chamber was unfired....(??)
ryder021970
08-03-18, 02:59
Most of the comments here say that this is a ruptured case. Maybe that is what happened; there also could have been a sharp thing in the mag ( I dont know ) that may have hit the primer....
An AR cannot fire out of battery. The hammer cannot strike the firing pin, and out of battery means the firing pin cannot protrude through the bolt face and contact the primer.
Well, now it sounds like a slam fire? Could the primer have blown out and caused this?
But he's saying that the round in the chamber was unfired.
OP, was there a ruptured case at all as a result of the mag blowing? An 1/8" slit near the ejection groove of the case from the mag doesn't seem sufficient to cause what is being described.
And in the end we're probably never going to know what really happened. If a cartridge actually was detonated IN the mag, it's the first one I've ever heard of.
Maybe the round in the mag with the split case had the split case already before the incident. Real shitty reload. So it was spilling powder everywhere or at least had exposed powder. Sometimes some Sparks and flame get into the upper receiver while firing. This could set off this round with little damage to anything.
Without pics it's all just speculation, but this is the only way that a round going off in the mag seems possible. There is no way a round cooks off in an ar mag, that is ridiculous.
To have a "cookoff" in a firearm, the mass of the gun metal in contact with the cartridge has to be large enough to attain and retain a massive amount of heat. That is why cookoffs are fairly common in air-cooled machineguns* and have been known in semi-and full-auto rifles, but are rare (if known at all) in handguns. Two factors are against it: 1) the mass of the gun is not enough to absorb and retain the heat needed, and (2) the magazine needs to be removed and replaced instantly, with an almost endless supply of loaded magazines kept ready.
To "cook off" a round, the receiver and chamber area of the barrel has to be fired almost continuously until it is near red-hot, but then has to be stopped with a round in the chamber and kept there long enough for it to attain firing temperature. A handgun "cooking off" from firing? I think I would call that one "busted."
ryder021970
08-07-18, 19:35
I agree that without any more detail than what is available, we cannot really say what happened. A damaged casing exposing the powder and that powder catching on to some spark also sounds reasonable but the RO and shooter both claimed the round in the chamber was unfired. Perhaps a primer that was not seated properly caught on something and ignited.......
I agree that without any more detail than what is available, we cannot really say what happened. A damaged casing exposing the powder and that powder catching on to some spark also sounds reasonable but the RO and shooter both claimed the round in the chamber was unfired. Perhaps a primer that was not seated properly caught on something and ignited.......
No offense, and not trying to be argumentative... but powder needs a "chamber" to "behave" like a propellant.
I don't think that a brass case could readily be a substitute for a chamber. In other words, the powder wouldn't burn properly or fully enough to create full pressure.
Much like throwing ammo into a fire, the rounds would fizzle rather then be allowed to produce peak pressure, primers pop out, and bullets pop out first... as opposed to when they are fully chambered, only then can powder create full pressure.
It is possible the primer detonated, ( IMHO, no matter how unlikely ) and popped out , while igniting some of the powder.. not enough to cause a full on kaboom, since again the powder wasn't in a pressure vessel ( chamber ) and while the bullet had no room to pop out, the case split... releasing pressure.
I suspect the whole story has become confused.
If the bolt is out of spec or the headspace is improperly set, an OOB detonation is completely possible resulting in a case head separation, blowing out the magazine and (sometimes) destroying the upper reciever. I have seen it happen.
A case head separation is not an out of battery detonation. An AR can not fire out of battery. Full stop.
The theory still works even though there was an unfired round in the chamber. Like this, shot fired, bcg to the rear, empty is ejected, next round is fed as the round underneath gets lit.
I agree that without any more detail than what is available, we cannot really say what happened. A damaged casing exposing the powder and that powder catching on to some spark also sounds reasonable but the RO and shooter both claimed the round in the chamber was unfired. Perhaps a primer that was not seated properly caught on something and ignited.......
I think cookoffs are myth. There's a video of a guy firing a m4 full auto, reloading as fast as he can. Rifle stopped when the aluminum gas tube melted. No cook off.
I don't think the gas tube was aluminum.
Gas tubes aren't made from aluminum.
I think cookoffs are myth. There's a video of a guy firing a m4 full auto, reloading as fast as he can. Rifle stopped when the aluminum gas tube melted. No cook off.
I'm thinkin a case rupture too, also if it blowed everything out through the magazine with no damage, wouldn't the floor plate be broken or even the mag since it slides on a lip? also on cookoffs, I have run a lot of rounds through full autos and never had one. Not saying it's not possible, just saying I've had them really hot before.
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