The USC is the bastard child of HKs modern long gun line. It’s comically long, the stock is corny, and the mags are limited to 10 rounds. In order to get it to ‘true’ UMP status you’re looking at a grand total of at least $3000-3800 in gun/parts/labor. And to be honest it’s not even that great of a gun even when it’s done.

But it’s an icon of my gun-loving childhood and I still felt the itch. So with that said, here’s how I took an otherwise homely USC and got it a hell of a lot closer to the gun it was intended to be.

1) Buy the USC, they can be had as cheap as $1150-1299 on various sites/Gunbroker. Let’s face it, they ain’t fast sellers

2) SBR it. Eform1 turnaround times are in the teens-of-days and it’s super easy. $200.

3) Chop the barrel. I opted to have it threaded, which costs a little more($150), but the extra budget minded could have a basic cut/crown for $50. Shout out to Andrew at Atwell Tactical who did mine. And my PS90 SBR.

4) Buy some rails for the top and sides, they can be found for anywhere from $50-100 for the set if you browse HK classifieds here and there.

5) Buy some 15 round mags to supplement the factory 10s. They’re ProMag (I know..) but they’re 100 percent reliable over 500+ rounds so far. If there’s anyone who could screw up a single stack direct blowback mag it’s ProMag, but I don’t know what to tell you, these work.

6) Here’s the part that sucks the most, but highly worth the effort if you’re even halfway handy. I used a hacksaw to cut through the lower spine of the stock, a dremel to carve away the inside ‘bridge’ of the stock, and a heat gun to reshape the bottom spine up into a more UMPy position. A couple of subtle screws to hold it in place and some JBPlasticweld later and it looks about a thousand times better than the original thumbhole abortion. Cost $8 and about 2 hours time.

So for about $1650 (including the tax stamp) I’ve got myself a “poor man’s” UMP. It’s fairly accurate, the trigger sucks big time, and the recoil is disproportionately heavy compared to the round it fires, but it’s also supremely reliable and cool as hell. Which basically sums up every HK currently made.

Before:



After:

Wow.  You did an amazing job with the stock.  Congrats.

Seriously awesome job OP. Honestly I would rather hump a piece of splintered balsa wood than ever depend on Promags.

Just buy an Extar, or better, an Extar EP45

Very nice looking gun. Tell us more about how you reconfigured the stock. That came out really nice.

@patw

To be honest, I didn’t have a whole lot of confidence in how this project would turn out, so the execution was a little bit rough. If I would have known it would turn out halfway decently, I likely would have attempted to make the plastic glue lines a bit cleaner, and possibly not used the bulky screws.

Either way, I used a hacksaw to make a cut at 1, then a dremel to cut at 2. I used the dremel grinding wheel to slowly smooth away the remaining material under cut 2. Then sanded the area smooth. I then used a heat gun at the back lower corner of the stock nearest the little sling swivel thing as I gradually deformed the lower stock bar upward to meet the rest of the stock near the receiver.

All the while I was slowly making dremel grind cuts to the material above cut 2, to allow it to meet and more or less sit flush with the bottom spine of the stock as I gradually heat-gunned it upward.

Once the heat gun had it fairly flexible, I used a clamp to hold it in place while I drilled two pilot holes into the underside of the stock and screwed it into place. Once that was all done, I used the JBplasticweld (black) to cover the gaps since inevitably my dremel job wasn’t perfect. Then I dusted the area with black high-heat BBQ grill paint and let it dry/set for 30 min or so.

Oh and then I went back with the same dremel/fine sanding and smoothed over the back of the pistol grip where the stock used to attach

Really nice job reconfiguring the stock...WELL DONE!

Thanks for the update. It still looks really good and those things can be easily rectified, so all in all a nice job.

Nice, thx for the write up

That looks good.  The stock re-shape was nicely done.

The Promags evidently do well in the USC - I have a UMP clone, from a parts kit and Omega receiver - the USA made UMP mags at HK-USA have been hit or miss for me.  They either work 100% or jam every other round.  German mags are expensive but 100%.

German made UMP mags are often $100+ so if you can run on promags, good.

I will say the promag HK93 mags also work well, despite being not too attractive. Promag can make a good mag sometimes.

I want a HK433/437. Where do I sign up?

Strangely the Promag P320 mags are what was recommended to me by B&T for the P320 lowers on the GHM9 and APC9. I reluctantly bought 10 of the 32 round mags and they have been flawless for a few thousand rounds now. While not directly related to your UMP I noticed your comment about the Promags.