This is something you hear about often, and I haven't heard whether it was factual or not. But looking at it from an engineering standpoint:

Of course polymer will melt before steel. You don't have to be the night time manager of 7/11 to know that. So you can imagine that HK's engineers knew what issues stood before them when designing the G36 and UMP series. First thing they probably did was decide what kind of heat the gun should be able to take. In the suppressor world, it appears that "a gunfight" is classified as 8 mags through a gun, alternating semi-auto and full auto between magazines, and maintaining a rate of fire of 2 shots per second in semi-auto mode. In a suppressor test, a durable suppressor is expected to absolutely last that test, then allowed to cool, and then repeated a number of times to see how many fights the silencer should last before it is replaced.

To imagine that HK engineers did not put the UMP and G36 through similar tests is a little out there. I know people love to play "Monday morning engineer" all the time at gun stores, but if it's easy enough for Jimbo Clerk to understand, it's probably been thought of by a designing firm as good as HK. And even if the designers didn't catch it, the thorough testing would.

After they figure it all out, a safety factor is thrown in to make sure everything is okay.

My guess:

The story isn't BS, but it is exaggerated. Perhaps they ran this gun for an hour and shot many, many, many rounds. And in that short range session, they actually simulated 3 or 4 "gunfights" without ever letting the gun cool down. So the gun, being pushed farther than what HK designers felt was a reasonable amount of rounds in a fight, began to have problems. And as the HK rep said, "You guys HAVE to let the gun cool down every now and then if you are going to do 40 mag dumps in a row. And since you're in South Texas/California/New Mexico/etc, it'd be best to let it cool in the AC."

Thus the guy starts badmouthing HK because he pushed the thing too far and preaches that plastic is better suited for milk jugs.

My guess.

 

I just don't know about that one, but I've wondered the same thing. On one hand, I agree with Maverick, I just can't believe that HK would produce something made to run in full-auto that could still melt with relatively little consecutive use.

But on the other hand, the last time I took my HK53 to the one range in Dallas I know of that allows full-auto, I shot I think 10 magazines, so 200 rounds in all, in maybe 15 minutes. The first 8 mags were a mix of single fire trying for accurate groupings, short 3 or 4 round bursts, and a few half-mag dumps. I only brought 5 mags, so it got a chance to cool a little while I reloaded. I only dumped one full magazine, the last one. About that time I noticed smoke coming from under the handguard. I took it off and like a moron when a waiter sets down a plate while using a hot pad and saying "careful, hot plate", I touched the barrel. My skin sizzled. I tested the flash hider in the case and it would have definitely melted the cordura of the soft case.

I'm sure it was hot enough to melt plastic had there been any around the trunion. I can't understand how the UMPs can handle this, unless maybe they're made of the high-temp nylon and the gun case is not. But even so, the high temp nylon can't take THAT much more heat than the regular stuff. I've wondered why they didn't make it out of some of the much more heat-resistant thermoset plastics like phenolic or something.

 

From my own work with glass filled nylon and other composites, depending on fillers, catalyst, molding technique, and a million other factors...

I would guess the UMP's housing to withstand anywhere from 500º-650º occasionally, and way less sustained (like 450º if being used).

While I don't think the gun is liable to melt on you at the range, depending on the actual manner of abuse, I bet you could F some S up if you tried hard enough. If you heard skin sizzle, I bet that was above 500º, but there you are talking an all steel gun that retains heat well. The only thing that should heat on the UMP is the barrel and trunnion, and most of the barrel floats so it should diffuse quicker then a steel gun.

I have a love / hate with the UMP. On one hand I think it looks cool as hell. On the other hand, I recognize a disposable/economy item when I see one. The UMP is cheaper then the MP5 it replaced in every single aspect. If it melts under extreme abuse then so what, the PD/Gov owner will just buy another one. This is of course not the case for civis, but I doubt many civis with UMP conversions have the resources to abuse one in this way.


I agree that the story MAY have some merit but I don't think you're hearing both sides. Also, I have put off my own UMP build due to a few factors with the weapon system not being nearly worth what people are paying (the plastic bothers me less then the parts availability and the heavy bolt / simple blowback system).

 

Polymer will melt @ three times sooner (quicker) than steel. That much we know. If the polymer surrounding metal parts is subjected to heat in excess of its melting point the polymer will soften. If the wrong polymer (and enough of it softens) the parts can in fact shift in their position and could potentially result in stoppages or the barrel alignment problems noted. Now I do not know about the facts of the report provided but I did witness a single G36 rifle fire nine (9) 100-rd Beta drum magazines (900 rounds), all in full auto (one continuous burst per mag) as fast as the mags could be loaded. All rounds were fired by a single shooter in less that 3 minutes from an unsupported standing position with many witnesses (US Govt also) there and a video camera running. The weapon fired each and every round without a single stoppage. In fact @ the 800th round the edges of the polymer handgun around the barrel began to burn - flames were present. The operator had to fire the last two mags with one arm using the non-firing hand to shield his face from the heat. No rounds exited from the side of the barrel (that happens is US Govt tests with an M4 barrel @ 570 rounds), a far greater concern, like cook-offs-then melting polymer.

In an abusive test scenario as described above even a rifle-caliber weapon like the G36 will "melt" but in this case as described the weapon never missed a beat. The weapon was functional after cooling. I do not know about and change in POI or accuracy but like the UMP scenario that started this thread this can be considered abusive treatment for any SMG or rifle regardless. The operators must take some common sense actions to prevent this (ambient cooling, forced air cooling, even in water as HK does in past desert testing) and the high chance of cook offs that will occur long before polymer melts which is a greater and more serious safety issue for both operators and bystanders.

Respect of the weapon seems absent in this account. Too hot to hold, too hot to shoot. Don't be dumb! If you need a LMG get one. And all should note most LMG's are not made from polymer!

G3Kurz

 

Respect of the weapon seems absent in this account. Too hot to hold, too hot to shoot. Don't be dumb! If you need a LMG get one.

I wish I had an animated gif of a golf clap. Well put. Just because you CAN doesn't mean you SHOULD.

 

I watched a you tube video a while back of a G36C , the guy did 8 beta mag dumps in a row with no break in between and the gun was still fine . That is definitely enough to make most normal guns pretty upset .

 

It's plastic, it will melt. Just like if you threw it in the campfire.

Sure it has design limits, it's not indestructible, nothing is.

Is the story BS? Who knows.

 

the question is, is it a thermoform or thermoset plastic? I would hope that they would not use a thermoform polymer as a heat shield, I would expect that of tapco not HK.

 

Thermorform is a process. Thermoplastic is the material type you're thinking of. The receivers are made of a thermoplastic, Nylon 66 I think. So yes, it will return to a liquid state ("melt") when heated.

I too wonder why they didn't use a thermoset plastic. I know they wouldn't be able to hot-stamp the date codes and proof marks like they currently do, but there are other ways they could have done that. There must be some other reason.

 

Friend of a Friend stories are usually 100% BS. I have a F/A UMP and have abused it to the max, 45ACP just does not heat up.

However there is a true story of a G36 with silencer melting. It was posted here on HKPRO (with Pictures) a few years ago and I am sure you could find it if you tried. I think the author was LARRYG36.