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Hk USC45 to Hk UMP45 Short Barreled Rifle build project how to and clone info page
HK UMP .45 / USC Conversion ::

HK USC to HK UMP SBR clone build project info and how to
This project is nearly complete. The main goal being to start with an HK USC and convert it into a semi auto, SBR ( Short Barreled Rifle ) version of the HK UMP 45. This conversion can be done in 3 calibers: .45 auto, .40 caliber and 9mm. For this conversion we are sticking with the original USC caliber, .45.

This is a fairly simple conversion if you have access to the proper machining tools and a bit of gun smithing experience. Some of the main points we will cover for this conversion are:

Section Highlights:

HK USC to UMP conversion and build services from Black Ops Defense: Click Here

Comparison of the HK UMP and USC 45 general conversion and build information
USC to UMP General Conversion Info ::

There are many ways to go about this conversion. Plastic verses metal stock blocks, real HK lower and mag well verses TN grease gun mag conversion, black USC verses gray USC and so on... We will be outlining how this conversion was done and how we did it. We will also touch on the other possible methods for those who might be interested but may not go into extensive detail. Just read below and look for links to the info you need!

Some of the major work that needs to be done here are modifications to the USC receiver. The USC is similar to the UMP but different enough to make the conversion more than just a bolt on affair. The USC uses a single stacked 10 round mag and has a fixed stock held on by screws. The UMP uses 25 round, double stacked mags and has a fixed stock hinge and folding stock. Also the UMP lower housing will not fit directly onto the USC lower with out a slight modification. The USC does not have the air vent slots around the barrel like the UMP. All though milling the air vents may not be a necessity, they greatly add to the authenticity of the clone build. We will explain and illustrate below how to modify the USC and UMP parts to make it all work.

There are legal ramifications to consider when doing this conversion. Since this is a none US gun 922r compliance and US compliance parts will apply. This particular project is being built as a registered SBR NFA weapon so 922r compliance does not apply. Some of the compliance parts and issues will be examined below for reference purposes. This info is for any one that wants to build a rifle or pistol. ( Always check your local, state and federal laws before doing any gun project to make sure the info is current and legal in your area )

HK USC to UMP conversion and build services from Black Ops Defense: Click Here

How to dye a gray HK USC black how to instructions and photos of dyeing a gray HK black
Gray USC to Hk Black / Dyeing Instructions ::

This process is not hard and quite in-expensive. Basically all your doing is soaking the synthetic / plastic material in extremely hot water and allowing the dye to set in. Using some sort of insolation to keep the temperature up and being sure that the parts to be dyed are clean.

What you need:

  • Rit clothing dye / 1 green and 3 black
  • Bucket or tub that will allow you to completely submerge your parts
  • Towels, blankets or some other form of insolation to surround and cover your dye tub
  • Stove and pots to boil water
  • Rubber gloves ( if you don't want black hands )

Simply boil water in multiple large pots ( or nearly boiling ), add hot water to your tub, add all 4 containers of Rit dye ( the green is to keep the color looking black and to fight off the purple you get when only using black dye ), add your thoroughly washed parts ( wash everything in hot soapy water and be sure all grease and oil is removed ) cover and insolate the tub for about 4 hours. Occasionally or once an hour, move the parts around a bit to make sure no air bubbles are present. After dumping rinse the parts until no more black leaches out. Dry the parts and re assemble!

  • Remove all black plastic parts as the process may turn them purple ish
  • The heat opens the "pores" in the plastic so rinse with cold water to seal and "close" them back up again
  • Oil may leave purple spots so make sure the parts are clean
  • Do the dye work after the machine work or you will see gray where the plastic was cut away
  • If you use 1 bottle of green and you keep your parts at a nice high temperature, you will have a nice black
    with no purple

HK USC to UMP conversion and build services from Black Ops Defense: Click Here

Stock block modification and comparison TN Top Notch verses HDPS metal stock block info and photos for USC to UMP conversion
Custom Stock Block Modification ::

These photos illustrate the modification done to the TN ( Top Notch, "grease gun mag lower") USC to UMP stock block to allow fitting of an HK UMP full auto marked lower trigger housing. No modifications were necessary to the standard HK lower. Using a block of black Delrin we were able to cut away part of the stock block and insert a block of milled Delrin to create the T slot needed for the correct UMP lower to fit. The TN stock block is nice but is designed specifically for the TN lower housing. The first photo shows the stock and stock block in its original form.

This was only necessary to make this stock block work with an original UMP lower. The other options would have been to use the intended TN "grease gun mag" lower or use the metal stock block available from HDPS. The HDPS block is the most durable and would require no modifications at all but is much more expensive. In this case we chose to do some work and save money.

So far it looks great and has held up just fine, If it fails in the future we will upgrade this piece to the metal HDPS stock block.

Top Notch USC UMP stock block set Top Notch USC UMP stock block set Top Notch USC UMP stock block set
Top Notch USC UMP stock block set Top Notch USC UMP stock block set Top Notch USC UMP stock block set

Since the above was written allot has changed. Top Notch ( TN ) now makes a stock and stock block set designed to fit the factory UMP lower. They are not quite as durable as the metal ones but seems to be a great option for doing the USC to UMP conversions. they are only about 200 bucks and count as 1 US compliant part. So far they have been great except for a few defective ones that had cracking plastic around the hinge pin. Not a big deal since Wade at Top Notch will replace it for you for free if you have this problem. So far I do recommend the TN set as an all around good way to go for your conversion. Yes, the metal ones are better and you can use an original HK stock but they cost more than double and you still need your 3rd US compliance part. So it does add quite a bit more to the cost of your build...

Top Notch USC UMP stock block set Top Notch USC UMP stock block set Top Notch USC UMP stock block set
Top Notch USC UMP stock block set Top Notch USC UMP stock block set  

HK USC to UMP conversion and build services from Black Ops Defense: Click Here

Comparison of the HK UMP and USC 45 general conversion and build information
USC to UMP Receiver Modifications ::

The USC upper receiver needs just a few modifications to do the conversion. Dying from gray to black, if you have a gray USC. ( detailed above ) The magazine well milled out to accept the larger UMP mags and the cooling vents milled into the for-end.

The magazine well is actually pretty easy to do. We are machining the opening with a mill but it could be done with a dermal tool or something similar and filed by hand to clean it up and finish fit the mag. Basically with the UMP lower attached to the gun just look up into the mag well and you can see the area that needs to be removed. You could even trace it out with a pencil and use that as a guide to remove the plastic. This process is not extremely curtail and there is a good bit of tolerance. You can always precut it conservatively and keep filing until the mag fits just right.

Milling the cooling vents is a bit tricky. Plenty of tolerance since they are basically cosmetic but you want to make sure they are completely straight and parallel with the other lines of the gun. I would recommend a mill for this job but a milling table on a drill press may work also. be carful when clamping the receiver. You need it to be tight but you don’t want to smash it. A block inside the gun to help support it in the vice is a good idea. The bolt helps, if you put that in the gun before clamping it down.

pics and measurements coming soon::

HK USC to UMP conversion and build services from Black Ops Defense: Click Here