Everybody talks about it, and in fact my Mini-14 manual warns about it. Even in full-auto, does it ever occur? There’s a video of someone shooting a M4 full auto with 100 round magazines–at the 400 round mark the gas tube melts and the gun stops firing, but no cook off. How about in heavy combat, e.g. Ia Drang? So is this a problem that doesn’t really exist?
It’s absolutely real. It’s happend to me twice on a 240B. Once as the gunner and one as an A gunner.
As for an m4 I’ve done 10 mag ammo dumps with about 150 people participating an didn’t see any.
Semper Fi JSOP
Happened to my 240G, ofcourse I had just run through 2 belts.
I guess I’ll join the dog pile.
Yes it’s real. It’s a real danger on the range (2-way or not), Especially with belt-feds. I have seen this more than once.
The way I understand it is, there should be no cook off as long as you keep firing the weapon, and do not allow a round to remain in a hot chamber for any length of time. It can only occur if a round has time to soak up enough heat for ignite the primer.
Yes, it happened to me with my SAW.
Pretty sure the same guy you’re talking about has a video showing a cookoff…
same here we did the old twisted the belt trick when it started to run away
Isnt it a bad sear that causes a run away not a hot barrel?
It’s always like the perfect storm of malfunction when a cook off occurs in a open bolt. Hang fires are scary as shit!!! Especially when you think it’s a jam and open the cover.
Cook-offs are real, can be duplicated, and seen on youtube.
6 mags in less than 5 minutes from a non-SOCOM barrel M4A1 will cause a cook-off. Or at least it did with me.
Yes, cook-offs are real.
I once had an M-60 cook-off while training troops in Thailand. A bad extractor left a round in the chamber after firing several belts on a sweltering day. It fired one round.
Okie John
Since we’re on the subject, can someone explain to me what it means to pop primers? There was an episode of Sons Of Guns last yr where they ran like 2 or 3 drum mags through an AR type till the gas tube glowed bright red. Near the end or in the middle somewhere, a primer hit Will on the glasses.
So I know what the result is (a primer pops off the shell). My question is when does that happen? Is that off the spent shell? I don’t think it can be on an unfired round because the gun didn’t malfunction, it kept going.
So if my assumption above is correct, what causes a primer to pop off a spent shell? Thanks in advance.
Someone told me once that it had to do with overpressure and the primer not being installed correctly. Personally Ive only seen it on blanks.
As for Sons of Guns, I hear they’re making an AR15 that will work in the desert.
I didn’t know they haven’t been working in the past 10 years…
Can someone explain to me how it happens with a belt fed like an M240 or M249 considering they fire from an open bolt?
I understand that in some weird way it could happen, but I have never seen it.
With the M2 .50 I have seen it because it fires from the closed bolt position and the round sits in the chamber. That is also why you aren’t supposed to exceed the max sustained rate and why you swap barrels.
M60 will do it when the gunner bitch fingers the trigger enough to wear down the sear and or operating rod.
Basically there’s nothing left to stop the bolt from flying, so it runs until it expends all the rounds, jams, or someone breaks the belt.
Every once in a hwile you get some dumbass who assembles the trigger group incorrectly after cleaning or doesn’t safety wire the leaf retainer with trip wire so the trigger group can come loose or sag, and the rounds start to go on thier own right after the first pull of the charing handle.
Dunno about M249 or M240 but have to imagine it would be a simular failure.
Its usually during a malfunction or user error more often then not its the user in some form. Ive never seen one just randomly happen like I would imagine it being with a M2 or rifle of some sort.
In my experience on a weapon that’s prone to misfires they’re common obviously because the bolts not getting locked back.
I dont think it could happen on the feed tray Ive never seen the heat transfer like that.
Someone once told me that slugish op. on a 240 was caused by the round firing off milliseconds to early due to heat. I took that with a grain of salt and stuck by thinking it has to due with heat and expansion and lube.
Maybe you can clarify.
Soldiers (at least from what I’ve seen) Routinely disregard ROFs or changing barrels.
I can’t tell you how many automatic rifleman in country who didn’t carry a spare barrel.
IIRC, even if you don’t expect a cook off, it still makes sense to empty a hot chamber when you’re done shooting. Because heat can change the ball powder and make it clump together and affect several characteristics upon ignition.
Same idea as not leaving an extra pistol mag in the glove box in summer. Your 140*F interior may fuck your ammo up. OR is that bullshit?
I have only heard of one actual “cook off” with an open bolt weapon.
I’ll see if I can dig it up.
A weapon must be PHENOMINALLY hot to get a round to cook off that is not in the chamber.
Most of what is being described here is from runaway guns/sear issues.
A cook off with the round on the feed tray is pretty much guaranteed to stop the gun since it will blow the feedtray cover open and the belt out of the gun (with 7.62, the one I heard about was with an M249 and apparently the det allowed the gun to continue to run).
There are several recorded cases (in addition to eye-witness) of premature detonation due to incorrect timing/headspace, and they are really ugly with 7.62 guns.
ETA, found the thread:
https://www.m4carbine.net/showthread.php?t=11211
Look for decodeddiesel’s comments following mine.