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Discussion Starter #1
I got the TN lower kit on my UMP conversion that I bought from someone on Gunbroker who had it all configured with the UMP lower, semi auto trigger group installed, TN stock block, and the US made TN folding stock. I was wondering if the HDPS aluminum stock block was a huge difference and if I could just swap out stock blocks and install my US folding stock on HDPS stock block?
 

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Discussion Starter #3
Oh geeez, so I guess the answer to my question is a hell no! lol The TN stock I have counts as one my US compliance parts. I would pretty much need the HDPS stock block, HK stock, and another US made part. Blah. Thanks for the info Lohe.
 

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Honestly I would consider doing the HDPS block and have the TN stock modified to fit it. I'm sure Tbostic or Chopstix Kid could do, the process doesn't look that difficult. It would probably be cheaper than getting the HK stock and another US made part. Both of the members listed are a bit busy so it might take a while though. Lots of talented folk around here who might be able to do it.
 

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Discussion Starter #5
So the main issue is just getting the folding stock to fit the HDPS block? Nothing needs to be done to the lower receiver correct?
 

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Well there are two roads.
One is getting the TN block to fit the lower. You would need to have a T block somehow grafted to the TN block.
I think this would actually be easier and less expensive but would require someone with either good plastic welding skills
like Tbostic or Chopstix Kid or someone who could machine something and bolt it on to the TN block.
The other road would be to get an HDPS block and modify the TN stock to fit the HDPS block.
Yes, if you decided to modify the TN stock to fit the HDPS block you would not need to modify either the
HK UMP lower or the HDPS block, just the TN stock. Does that make any sense at all, I feel like I'm typing in code or something!
 

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Discussion Starter #7
Yep makes perfect sense. Sorry for being such a gun smithing newb. :) When I eventually get the HDPS block I can have Ed do it. His work rocks and he's cool to deal with.
 

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I have not compared the lowers but I did not think the HK lower from the TN kit would work with the HDPS block.
 

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Yep makes perfect sense. Sorry for being such a gun smithing newb. :) When I eventually get the HDPS block I can have Ed do it. His work rocks and he's cool to deal with.
Don't worry about it, not many people have even had experience with the TN stuff, I don't think they sold them for very long?? I'm working on a few different things for mine; I think I've had the .40 kit and the USC for a year and a half now maybe a little longer and it's still not done! eek

I have not compared the lowers but I did not think the HK lower from the TN kit would work with the HDPS block.
Hope he can clarify but I was under the impression that he was going to use the HK lower and not the TN lower because if he was just going to use the TN lower why not use the TN block and stock. I'm pretty sure he would be set for US parts then.
 

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I got the TN lower kit on my UMP conversion that I bought from someone on Gunbroker who had it all configured with the UMP lower, semi auto trigger group installed, TN stock block, and the US made TN folding stock. I was wondering if the HDPS aluminum stock block was a huge difference and if I could just swap out stock blocks and install my US folding stock on HDPS stock block?
Not sure what you mean by the "TN lower"? Do you have the TN lower that uses M3 Grease gun mags, or a HK UMP lower that is modified to work with the TN stock block? If it's the UMP lower, you won't be able to reuse that with the HDPS stock block because the rear of lower is cut off to work with the TN stock block. The HDPS block uses unmodified UMP lowers.
 

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Discussion Starter #11
No I have an UMP Navy lower on mine (Safe, SA, FA selectors). I bought the whole lower kit completed from someone that used the TN stock block and stock, so it's possible the lower had been cut, as you say, to work with the TN stock block. I'm not sure exactly what part is taken off to be able to tell for sure though.
 

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This is the UMP lower with the HDPS stock block. Note that the rear of the UMP lower has a raised section with a hole for a pushpin, and that there is a tang to the rear of the pushpin section.

http://www.hdps.org/htm/UMP-combo-FBI-d.jpg

The HDPS block is cut at the bottom accommodate that pushpin and rear tang.

On the TN conversions, that rear section of the lower with the pushpin hole and rear tang is cut off and the bottom of the stock block goes all the way down. TN drills a new hole for a pushpin at the rear of the remaining lower section. You can sort of see the new pin in these pictures, just above the rear of the grip.

Examples Page 2

With the rear part of the lower where the original pushpin hole was cut off for use on with the TN block, the lower is no longer usable with the HDPS block.

If you have a picture of your lower, it would very be easy to tell.
 

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Discussion Starter #13
Ah I see what you guys are saying. Yea that raised part on the back of my lower has been cut off and I'm guessing they drilled a new pushpin hole to work with the TN stock block. Argh. Oh well. Thanks again guys. I mean I'm fine with what I have. It's pretty solid, but I was wanting to upgrade to the aluminum block when I got some extra money. Oh well...
 

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I would just stick with what you have then, I haven't heard a single case of the TN setup failing at all.
If you really want to go with an HDPS block you might be able to have a hole drilled in the HDPS block
where the hole is in the TN block. Not sure if that would work though but it would be pretty secure if it
did I think. You would have to buy an HK stock though, or one of the US made clones or have the TN
one modified which looks like a pain.
 
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