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Discussion Starter #1
Hello,

I have a USC that I'm about to do the UMP conversion on. I bought a rear stub/folding stock combo (it already had the pin installed) and an FBI lower. From my research I thought that was all I needed. When I went to my LGS today and talked to the H&K armorer there, he said the stub would not work and that I needed the HDPS stock block. I went ahead and ordered a stock block but my question is, if the stub doesn't work for the conversion, what is it for?

Thank you in advance.
 

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The UMP rear stub is used for the conversion type where the rear of the USC receiver is cut off and the UMP stub is grafted on by plastic welding the receiver. Not everyone has the skill or experience to do this properly and it's just likely that your smith has no experience doing it. The stock block conversion is much simplier and doesn't require cutting and welding the polymer receiver, and probably is the only conversion he's familiar with.

Just send your USC, lower, and UMP stub to Tom Bostic and he can do the job.
 

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Discussion Starter #5
Thank you very much guys. I will check out Tommy's website. I've had this rifle for about 2 years now and it's my favorite rifle. I'm excited to see what it will be like once I have the conversion done.
 

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get the fused stub job done by tbostic!
 

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To be fair, chopping off the rear of a USC and plastic welding a UMP rear on probably isn't something they teach at HK Armorers school, since it's hardly a HK approved modification.
 

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To be fair, chopping off the rear of a USC and plastic welding a UMP rear on probably isn't something they teach at HK Armorers school, since it's hardly a HK approved modification.
No part of a USC to UMP conversion is an HK approved modification.
 

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Discussion Starter #11
After checking out Tommy's website, I see he does great work and is highly recommended, but I cannot afford to have the fused stub conversion done. I ordered the stock block from HKparts.net and it should be here Friday.

Renegade, that UMP looks very nice!
 

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I am just starting down the same road with my USC45. My initial thought was to go with a fuse job but as you have discovered, it ain't cheap. I have emailed Tommy Bostic with a few questions and in the meantime, I'm researching different ways to be 922R compliant while using the chopped factory barrel. Whatever option I choose, I'll let Tommy do the milling and fitting.
 

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Discussion Starter #13
Hi meh92,

For the 922R compliance, you can buy an American made USC magazine. I got 4 of them from HKparts for $50 each. From my inspection, they are just as well made as the German made magazines and are quite a bit cheaper. I haven't had a chance to try them out yet, but will do so once my conversion is finished.
 

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Hi, all. I will soon be starting on a USC-to-UMP (.45) conversion. I will do the "basic" stuff myself (rail, change the guts of the lower, stock block, etc), but will be working with a local gunsmith for the machining bits. I do have a quick question for those more experienced here.

When changing the lower, do I need the full lower (link to hkpart) or can I get a "stripped pistol grip" lower (link to hkparts), UMP lower backplate (link to hkparts) and stock block (link to hkparts)?

Thanks in advance for any insight you can offer!
 

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Yes they will, but you will need a UMP mag catch and likely a US-made trigger for 922r compliance.
 

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You will need to get the wider UMP mag catch pin (along with the mag catch), the USC is shorter. Also, grab an additional trigger housing pin. The UMP has an extra hole.

You do not need the UMP backplate if you are using the HDPS stock block. It takes the place of it.
 
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