The Heckler & Koch UMP (short for "Universale Maschinenpistole") is a submachine gun chambered in .45 ACP, and is developed as a cheaper, lighter variant for the Heckler & Koch (later HK) MP5. Boasting more stopping power because of the larger caliber, and a slower cyclic rate to keep things in balance (.45 kicks a lot compared to 9 mm), the UMP is favoured by US Customs and Border Patrol.
The first airsoft UMP I was introduced was the Guay & Guay (later G&G) UMG (short for "Uber Machinegun, lol), back in 2008 (if my memory works correctly). It was a really good SMG overall, there were some major issues first but G&G fixed them in later versions. I absolutely adored it, even though the name was silly (for licensing reasons, obviously). Is it strange, that HK allows manufacturers to copy the design 1:1, but it buggers them off real bad if the same manufacturer uses the correct name? I have always found that strange.
Be that as it may, not long after the G&G UMP-replica was released, Chinese manufacturer Double Eagle (later DE) rushed to copy it. Naming it plainly as the M86 (which is the standard procedure with DE:s guns, I have the M6 which is a copy of the Maruzen APS-2, the M58 which is a copy of the Marui Benelli M3 Shorty and the M81 which is a copy of the Marui USP AEP but more tactical), it is the only airsoft-UMP I have experience with besides the G&G-variant.
There is an Umarex UMP as well, and it boasts real trademarks (which it legally can, because Umarex has an agreement with HK). I don't own that one, but since the price is exactly the same as DE:s gun, I wonder if it's just a rebranded DE (I know for sure Umarex rebrands a lot of stuff, for example Vega Force Company's and Kien Well Company's guns).
I have owned the DE UMP for some time now, but I remember when picking it out of the box I was really surprised by a lot of stuff. Here's a list:
-The gun felt rock solid, like a plastic brick (which it should be, actually, because the real-steel counterpart has a polymer receiver!)
-The folding stock is really sturdy (I have managed to break numerous AK folding stocks, from all the manufacturers out there, this one, not so much!)
-With a 7,4 volt LiPo-battery the fire rate is close to the real gun, which means it's sloow!
-I got the urge to go and play some Counter Strike and rush B!
The fire selector of my gun broke off on one side (it's supposed to be ambidexterous, but now, forget it), and the remaining selector on the guns left side jumps from full auto to semi auto because the gun vibrates a lot when shooting. I have to keep it pressed downwards with my thumb if I want to use full auto for prolonged periods of time. Well, this isn't an issue, because I only play at CQB-arenas which have banned the use of full auto anyways, so it doesn't bother me much. A problem still.
Another problem, this one more severe. The cocking handle jammed mysteriously, and it is locked now in front position (no HK slap for me). I have absolutely no idea what causes this. If I open it up someday, then I'll see.
One more problem. One of the metal rails it has (the lower-one), broke down on mine. Crappy pot-metal, I'm sure. The other rails have survived the test of time, but I removed them as well (it's now even lighter and more streamlined).
It's a good replica of the famous UMP SMG, and it uses a normal Version 3 gearbox so upgrading/maintenance isn't an issue. Good bang for the buck, if one can't afford the more high-end G&G-one. I have painted my own with camouflage-colors and done some minor modding, like for example replaced the Tamiya-connector it comes with to a better Deans-one.