Ruh-Roh. Open Bolt Machine Gun Clearing Goes Hot With Cookoff

For those of us so blessed to have served with open-bolt machine guns, we know that clearing malfunctions can be a real chore. Where standard shoulder-fired small arms like the M4 are truly difficult to get to cook-off temperatures, belt-fed weapons can get to those short, fast, and in a hurry. In fact, this is the very reason why (including accelerated barrel wear) that most belt-fed weapons have a provision for quick barrel changes.

Most carbine users do not take into account the temperature of the barrel at all. In case of class 4 malfunctions (double feeds), soldiers are taught to immediately start remedial and later rectifying action to clear the issue. However, doing this with a belt-fed can be hazardous to your health in a training environment, as cook-offs are far more likely.

One ISAF soldier learned this the hard way. According to the video posted by SAM K, the hapless soldier was treating a Marine at Camp Leatherneck to some good German MG3 / MG42 action. The weapon malfunctions and the soldier immediately started clearing the malfunction.

While following some solid remedial action, the soldier forgot one thing – that a hot weapon is indeed a dangerous one (pun intended). While doing the correct remedial actions, he forgot to let the weapon cool. By forgetting this critical step, he took a face full of premature detonation.

Fortunately, the cheek scar will be the lesson learned. No other injury was reported.



TFB’s FNG. Completely irreverent of all things marketing but a passionate lover of new ideas and old ones well executed. Enjoys musing on all things firearms, shooting 3-gun, and attempting to be both tacticool AND tactical.


  • Alex @Sea

    Hope he wasn’t hurt.

    • TheNotoriousIUD

      Maybe hurt a little.
      He wont ever forget again.

  • Gary Kirk

    This was posted here not too long ago.. But it was before you joined..

    • Johnsmyname

      Agree with both Gary and Alex.

      Did we ever get a report on the guy? At least he had glasses on.

      • Gary Kirk

        He was training with Marines.. The corpsman gave him 2 ibuprofen and a bottle of water.. No problem!!

        Am I right devildoc

        • USMC03Vet

          Walk it off. I’m all out of Motrin.

          • Anthony “stalker6recon”

            Marines get motrin? As a soldier, it was “drink water, drive on”! We never got pills/meds……

        • Joe

          “Motrin and Water. Maybe a Band-Aid, if you’re a p***y.” Army was the same. Maybe Airmen get actual treatment?

          • Gary Kirk

            Motrin is ibuprofen.. Guess y’all at least got name brand.. Ours just appeared out of the corpsman’s bag, unless like USMC03 said.. “I’m out”, and that could mean he was.. Or just didn’t feel like looking for one..

          • Marc

            There’s a reason they call it the ‘Chair Force’.

          • Redfoot

            Eh, the infantry did not seem to mind when I was stitching them back together, running IV’s full of morphine, removing their toenails, helping to deliver their children stateside, and treating their chlamydia caught from the desert queens.

            Marc, I told to you that eventually the antibiotics won’t work anymore. Hope you finally listened ;-).

          • Nicks87

            No, we just know proper malfunction drills for belt fed weapons. Like putting a sand bag over the top cover and waiting for the gun to cool off, then use a cleaning rod to pop out the stuck round. No need for treatment if you dont get hurt. 😉

    • Dougscamo

      I’m cool with it….didn’t come here until last September…..

  • Jeff Smith

    Hasn’t this been posted before? I say this because I’m pretty sure the only reason I know that US soldiers are taught to lower their heads while clearing an open bolt malfunction (protecting themselves by putting their helmets between the gun and themselves) is because this video and what I’m pretty sure was an article on TFB.

    • Anonymoose

      Helmet? What helmet?

      • noob

        well at least he had eyepro when he was using his face to protect his scalp from getting cut by bits of flying brass.

  • Brett baker

    Ouch! All I can say is, glad it wasn’t me!

  • Phillip Cooper

    Is it 2014 again?? This has already been reported here, years ago..

  • Gun Fu Guru

    Cheek scar? Lucky båstard. Ladies love scars.

  • DanGoodShot

    I wish it was me. Cause that would mean I had my hands on an actual MG42!! I’ll take a kiss to the cheek for that. Not to mention the cool guy scar that comes with it!

  • Raginzerker

    So don’t do that when shooting MG’s, got it.

  • mosinman

    this is a repost

  • tiger

    This may sound crazy, but why not re invent the water cooled MG? Instead of a heavy jacket, why not copper tubing and a battery or solar powered motor to run coolant though the gun.

    • Darren Hruska

      A.V.P.M. Berthier may have had the answer over a century ago, but nobody bought it.

      • Sunshine_Shooter

        They would have sold more if they included one of those sweet hats!

    • Sunshine_Shooter

      The pump to circulate the water would need a really big solar panel. Maybe a battery powered pump charged by solar would be feasible. I don’t know why we don’t use water jackets any more.

      • tiger

        I’m talking only a maybe 3v sized motor. So yeah, a pair of AA batteries would work.

        • Sunshine_Shooter

          Hadn’t thought about that. Yeah, just use some AA batteries or whatever batteries those guys are already carrying for their optics and night vision and lights, etc.

          • Iggy

            They’d still be too heavy for infantry use, but I reckon a modernized
            vickers would make an excellent vehicle mounted gun. And that would
            also provide power for water circulation.

          • Sunshine_Shooter

            I thought about that. How heavy is an extra barrel? And while both combat heat, the water jacket doesn’t require the time spent without a usable weapon, even if it is measured in seconds.

          • Iggy

            Well if you can keep the water circulating, a vickers will happily keep shooting until the barrel is shot out, so I imagine having 10,000 or so rounds uninterrupted is pretty useful to have if overkill. And adding electronic assistance to that Bertheir style light jacket shown above (really cool btw) would keep the weight and profile down, while probably being almost as effective. (powering still probably to heavy for infantry though) Also advancements in optics means plunging fire could be brought back as way to more precisely deal with snipers and suchlike at a distance in urban combat without having to blow the crap out of a building.

          • Sunshine_Shooter

            You say too heavy for infantry, so I’ve converted the spare-barrel weights for M249 and M240 as gallons of water (since they are carrying this weight already). This doesn’t include the extra material needed for the jacket itself (to contain the water), but that could be compensated for by using less water or removing some other heat-necessary material from the current guns and/or barrels.

            M249 barrel weight: 4.05 lbs, or .50 gallons of water
            M240 barrel weight: 6.61 lbs, or .83 gallons of water

            Now, how much water is needed to keep these guns up and running? I have no idea. That would probably be dependent on the soldier’s loadout. I also think that MGs should be crew-served, which would mitigate both the weight and ammo issues to some degree, but I guess the modern Army disagrees. The modern Army also thinks that we should switch back to .308 as our primary round, so I’m not interested in their opinions.

          • tiger

            How heavy is a fish tank pump? How heavy is a Nascar drivers cool suit? With the right tools & some gunsmiths helping, I could build this to work.

          • Sunshine_Shooter

            Just came across some revelant info. At 750 rounds per minute, a 249 needs to get a barrel every 750 rounds. A standard load out for said soldier is 800 rounds. He could link every round together and blow it all out in 60 seconds and be out of ammo right as he needs and barrel change. We don’t need to make the heat system lighter if there isn’t a reason for it.

      • Ευστάθιος Παλαιολόγος

        Or maybe a generator harvesting the energy of the weapon cycling. I mean like taking advantage of the bolt recoiling.
        But, for dismounted infantry use, the main issue would still be the ammunition weight. So, maybe because you can’y carry much ammo anyways there isn’t any actual nead for watercooling the barrel?

    • mechamaster

      Umm, for General-Purpose Machine Gun role, the portability by infantry is the priority, that’s why the Infantry belt-fed machine gun has the capability for Quick-change Barrel… So the water-cooled is no go.

      * Well, you can add passive cooling system like the PKP Pecheneg with radial-cooling for example

      It seems the MG42 / MG3 design barrel change is more hassle ( you can only do it with heat-insulated glove to pick that hot barrel ) plus the rate-of fire is higher than FN MAG / M240 and M249 for example.

      It’s different story if the machine gun is in fixed emplacement configuration, the water cooling is beneficial in this configuration.

      • tiger

        I Picture a light weight active cooling system. If we can build a AC unit for a space suit, why not a MG? Perhaps a water & glycol system . Not sure. I want to get the same results, without the heavy water jackets of old. The Maxim , Brownings & Vickers of old worked well. But I want it to be portable too.

        • mechamaster

          Well, maybe with emerging exoskeleton technology, it would be practical to carry the active water cooling system.
          Without that, it’s heavy and affecting infantry mobility and stamina.

    • jcitizen

      You don’t need a pump – the boiling action of the water moves it in and out of the jacket and into the overflow can, and back again. Just and old coffee pot – convection does the work as the steam condenses.

      • tiger

        I wanted a pressurized active cooling system over that method. Even a R-12 refrigerant gas system in down sized form. The brainstorming continues. I want the same cooling but without the weight of the water jacket system of old.

        • AlDeLarge

          Anhydrous ammonia is usually used in small sealed remote cooling applications. Laptop CPU coolers, for example.

  • Sasquatch

    Um so no one seems to notice the mg 42 and how its not in a museum?

    • Dave

      It’s a MG3/MG74, a modern version the germans use in 7.62NATO. There is nothing special about them, thousands of them all over the place and in service today.

      • Sasquatch

        Yep false alarm everybody calm down! (Forgot about those lol)

  • snekrz

    I have a ’42. Granted its a semi but Im willing to bet they fired quite a string of ammo without letting it cool and most likely didnt have spare barrels handy causing a cook off. I want to say 5 belts or 250rnds was the norm for a change but I could be wrong. Popping the cover is not exactly first on the list for a misfire 😉

  • Ευστάθιος Παλαιολόγος

    I don’t remember the previous discusion.
    And maybe my brain isn’t working full speed right now, but,
    How do you get a cook off in an open bolt weapon? I mean, there’s no bullet in the chamber. A cartridge only goes in the chamber the moment it will be fired. The only case one stays in the chamber is if it missfires.
    But in this case the soldier clearly pull the bolt back so any remaining cartridge or case is extracted.
    Please can someone explain the mechanism of this incident?

    • Dave

      He tried to clear the jam without clearing the feed tray first, hence it slam fired without the top cover to hold the bolt and round on the track.

      • Andrew

        I don’t think so. His hand was on the charging handle pulled back and it didn’t go forward with the bolt.

    • mechamaster

      From the video, it’s something like the ‘hang-fire’ or delayed-ignition at first.
      The cartridge is in the chamber when the bolt is forward and doesn’t fire, so it take heat buildup from recent full-automatic fire.

      when he extract the round from hot chamber, the cartridge that absorbed heat-buildup ( and get cooked ) is exploded in the perfect time when he clean and inspect the chamber.

  • mazkact

    Painful lessons are not soon forgotten.

  • Mrninjatoes

    “By forgetting this critical step, he took a face full of premature detonation”

    Hot premature detonation on his face? Freudian slip? o.O

  • LazyReader

    That’s how red vs blue ended it’s season

  • Jim_Macklin

    Muzzle control
    PISS on it, it’ll steam and cool off

    An eye patch makes you look so “pirate like.”

  • Hank Seiter

    I have no experience with open-bolt cook-offs despite only having several belt-fed semi-automatic squad “machineguns” including a Yugo M53. They do get hot, thought! Thank God for ballistic eyewear. It looks like he may have taken a hit on the lower jaw or close to his jugular in his neck. Bad clearing technique fer sure.

    One time I did get what I thought was a slam-fire from a 5.56 because of a dirty chamber and the perfect storm of other mechanical failures that fired a round before it was fully chambered. Pretty scary. .308 would be even scarier.

  • Anthony “stalker6recon”

    From memory of being behind the M240Bravo, the correct method of clearing a malfunction is head down while opening/sweeping the chamber, specifically because of this. I never had one malfunction on me, and since that fires open bolt as well, I am very happy that I never did. I suspect that the most frightening open bolt shooter that I ever had the pleasure of firing a lot, it the Mk19. The second most frightening aspect of that weapon, was firing the ghost round at every loading/firing. I always expected a round to go down range anyway.