Gun Review: Converting an H&K USC to a UMP

It is no secret that H&K makes great firearms. They have been in business since 1949 and have produced a number of small arms that have been adopted by countless armies and police agencies across the globe. Perhaps the most famous however has been their MP5 series of submachine guns. The venerable MP5 fires from a closed bolt, which at the time was very unusual for a sub-gun, as open bolt firing had been the standard throughout the 20th century. The successor of the MP5, the H&K UMP or Universale Maschinenpistole was developed originally as a cheaper alternative to not only supplement, but replace the aging MP5s in police and military arsenals. Despite this, both weapon systems are still being produced, perhaps because the heavy proliferation and reputation of the MP5 has allowed the product to remain very profitable for Heckler & Koch.

Prior to 1989 a civilian variant of the MP5 was available to the public, dubbed the H&K model 94. It was imported with a 16 inch barrel to comply with import regulations and to be exempt from NFA registration as a short barreled rifle. Many of these have been given selective fire capability with the installation of a legally registered full-auto sear as well, making the MP5 one of the most common sub-guns in civilian hands despite the high cost. The ’89 ban on the importation of non-sporting rifles to the USA stopped the flow of H&K roller locked firearms (aside from the SP89 which hung on until ’94), and also prevented civilian variants of the UMP from ever reaching our shores. It seemed that us regular folks would never get to lay our hands on a UMP until parts kits from demilled guns and a little bit of innovation allowed shooters to convert their H&K USCs into UMP configuration. The following is a step by step process on how to perform this conversion.

First of course, you will need to purchase an H&K USC-


Buy a UMP lower, stock, and a “stock block” which is a magnificent piece of machined aluminum made by HDPS-


Enlarge these hooks on the UMP lower with a round file to allow them to fit over the USC’s slightly larger plastic pins-


Attach the stock to the stock block with a stock axle pin-


And throw it all together while being mindful of 922r-


To do it right, you need to mill the front out to form the cooling ports. Ed at HDPS performs front end milling and will mill the mag well out to accept the larger UMP mags-


Once you submit your form 1s, accompanying paperwork, and $200 check to the ATF and receive your tax stamp back in the mail, you are free to buy and attach your short barrel-


The gun also works great, even when firing it as fast as possible:

Storm also makes a delightful case that will hold the gun with an optic, odds and ends, and a total of six magazines!



And that is it! The conversion is very simple and only requires a total of three 922r compliance parts (I used a barrel, mag follower, floor plate, and sear just to be safe). As for the cost of replicating this build, I have compiled a list of my costs:

Gun- $1100
Lower- $400
Stock/block- $300
Tax stamp- $200
Barrel- $250
Vent cuts- $50

I also managed to sell my takeoff parts for $500 including the barrel, factory stock and lower, magazine, and buffer on a popular gun auction website. So all in all, I have approximately $1800 or so in this gun (sans optic of course).

So it is not a real UMP and never will be, but it is as close as we civvies will ever get to owning one without becoming an SOT. But you may be asking yourself, how does it compare to an MP5? Well, a quick accuracy test provided good results-



All shots were from 20 yards standing. So far I have put about 1500 rounds through this gun and it has yet to have any kind of jam or hiccup. I would highly recommend this conversion if you are in search of a fun project or a fun pistol caliber carbine!


Alex C.

Alex is a Senior Writer for The Firearm Blog and Director of TFBTV.


  • William

    Neat build but Ill lean toward a cheaper ar in 9

    • Alex C.

      Hey William,

      An AR in 9mm would certainly be more economical, but remember that a
      USC can be converted to 9mm and .40 cal with a barrel/bolt/mag. Also, if
      anyone has any questions regarding the conversion, feel free to ask and I
      will answer to the best of my ability!

      • Rusty Shackleford

        Good work, /k/ommando.

    • Until you shoot one:-)

  • GD

    Great article! I have wanted to do this for years. Now I have a renewed determination. Thanks.

  • SC

    Very interesting article!

    • Alex C.

      Thank you SC, I am glad you enjoyed it!

  • big daddy

    From an ugly duckling into one beautiful piece of weaponry. I just don’t understand how someone can find something so pretty scary and despicable. It’s gorgeous. I like the look much better than an MP5. I think the MP5 looks OK but the UMP just has a how can I say, just a hot body…LOL. I love the look of one. If I were abe to own a firearm I would have one like this in my safe. I live in New York City and we have to register just to get a can of pepper spray. I’m disabled so I can’t own a gun, do you believe that!!! As an ex driver of m113s, M577s and such I would have much rather carried that in .40 cal than the M3 grease gun I did.

    • You can’t have a gun because you happen to be disabled! That’s crazy.

      • big daddy

        Yes and I’m a disabled veteran too. Plus the hoops you have to jump through just to get a license. I am at a physical state that I cannot travel much. The offices are in places it’s so hard to get to and there is little parking, a lot of walking. It’s a horror to dissuade you from getting a license with fee after fee for your fingerprinting, the paper work and so on. It’s just not worth it. Plus it says right there in black and white if you have a physical disability it’s a no go to own a firearm.

        You cannot even own ones from before 1890. You cannot store any amount of black powder now (Fire department). So even a cap and ball which I have owned at one time and sold to a cop is a no go.

        So the people that own most firearms in the city are criminals. Mr. Blomberg who wants to limit our soda intake also wants us to be helpless. Yes rely on the worst shooting police in the world filled with Barney Fife types. The few times I had dealings with them many times they made me feel like the criminal. Some are really good, I have known some and met some really competent officers, but overall they’re clowns. An old friend who retired from the force used to call it high school with guns.

        So us New Yorkers only have our wits and whatever we can pickup to defend ourselves. I should have moved to Texas when I had the chance. New York state is different, it’s New York City that is the problem. I can’t even have a one shot 20 guage to defend my home.

  • Tim U

    Where did you find a USC for only $1100?

    • Masoo2

      I usually see them for $1400, so im not sure.

    • Alex C.

      Hey TIm, I bought the USC new in the box from a classifieds forum called Texas Gun Trader. The Gentleman that I bought the gun from was planning to do the conversion himself but instead decided to buy a transferable M16. In the end I got a great deal!

      • Tim U


        I hope I can be as lucky someday. Enjoy the awesome conversion!

  • Hami

    I built a similar HK SL8 to G36 conversion. Definitely turns heads at the range. Love the UMP too but I don’t think there are many USCs available at that price…

    • Alex C.

      Very cool, I have a g36 conversion as well, and an article is in the works!

  • Dale

    Now that’s an awesome conversion! I’m very impressed.

  • snake

    LOL @ 1.1k USC

    • Alex C.

      I must admit that I really lucked out on that deal!

  • roller-delayed*

  • wow, last time I priced a USC-> UMP conversion it’d cost me 3600

  • Shane

    Did you mean “convert”?

  • David Hansen

    Great post! A lot of useful information in here. I personally have never thought about doing this, but it might be worth it.

  • John184

    Now do this with the SL8!

  • n0truscotsman

    lets have a SL8 conversion to the G36! Ive seen a couple of those on the internet. Really neat.

  • wizardpc

    Where did you get the stock?

  • orion565

    I would love to know how you even got the gun for 1100, and the parts for so cheap. My convert was about 5k all said and done.