This section will outline the various types of USC to UMP conversions and options. This page will give you all of the information you need to decide which type of conversion you want to do and how to do it. This conversion can be done in 3 calibers: .45 auto, .40 caliber and 9mm. The gun can be built as a standard rifle or registered as an SBR (short barreled rifle).
This is a fairly simple conversion if you have access to the proper machining tools and/or a bit of gunsmithing experience. Some of the main points we will cover for this conversion are:
Section Highlights:
- Gray to black USC dye job/how to dye your USC
- Stock block type conversions and the various options
- Weld-on conversion/UMP rear hinge “fusion” type plastic welding
- USC receiver modifications
- FCG/lower trigger group options and necessary modifications
- Final accessorization
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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 is done and what the options are. 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 builtin 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. 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” that is not registers as an “SBR” or purchased originally as a “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 )
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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/Hinge Transition Pieces Available
The stock block or stock block type conversion refers to the transition piece that allows the folding stock to attach to the USC. This block bolts in place and gives the USC the necessary hinge to adapt the UMP folding stocks. This is a part you can purchase and bolt on in no time. It’s not complicated and requires no permanent modifications to your gun at all.
Some of the blocks are hinged to adapt the factory HK UMP folding stock and some are designed to work with other after market stocks. ( Bushmaster ACR, AR15 and others )
Finally you need to decide if you want a polymer or metal stock block. The main difference is price verses durability and US made verses HK or aftermarket. Pictures and links coming soon.
HK USC to UMP conversion and build services from Black Ops Defense: Click Here
USC Upper 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 careful 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.
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UMP Lower / Trigger Group Modifications
The lower options for the USC/UMP conversion are basically; Stock UMP lower modified or after market lower ( grease gun kit ). Both allow you to insert a larger, high capacity magazine and require the mag well cut out, in the upper receiver ( detailed above ). The factory UMP lower will allow your gun to accept the HK UMP 25 and 30 round mags. The grease gun kit works with the old WW2 type, M3 “grease gun” magazines ( 45 only ).
When adapting the UMP lower to the USC you will need to remove the rear buffer plate and enlarge the front hooks. The front hooks on the UMP are smaller so you will need to open them up just a bit to hook onto the USC. This can be done on a mill or you can just use a hand drill, about the same size as the front hook, and ream the hooks out with it. Just keep shaving material until it hooks on snugly.
pics and measurements coming soon.
HK USC to UMP conversion and build services from Black Ops Defense: Click Here
