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Discussion Starter #1
Alright. About to come into a partial UMP conversion. I want to have the rear UMP stub welded on but may be a bit til I get that done. Could the HDPS stock block B be modified to work with an un-modified UMP lower?
 

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You'd have to grind a groove about 2mm deep ,4-5mm wide ,and about 12mm long on the bottom of the block so you don't have to cut the nub off the rear of the ump lower that holds the ump buffer and backplate on.
 

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Discussion Starter #3
You'd have to grind a groove about 2mm deep ,4-5mm wide ,and about 12mm long on the bottom of the block so you don't have to cut the nub off the rear of the ump lower that holds the ump buffer and backplate on.
Is that possible without destroying the stock block?
 

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From looking at my UMP conversion, nothing was done to the stock block B. Mine has 2 chamfered cuts in the lower to mate the stock block B. The nub was removed on the lower as well.
Let me know if you would like to see some pics of what I'm talking about.
 

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I don't even know if it would have to be 4 mm wide. You could certainly do it without hurting the functionality of the block.
 

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Discussion Starter #6
Sure sixy. I'm just trying to think of a way to use the stock block temporarily without having to mod the lower. Not sure why HDPS didn't make them that way anyway.
 

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Yeah my lower nub dimensions were based on the 10 mins mine had itbefore I Razored it off a year ago, lol.
 

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Sure sixy. I'm just trying to think of a way to use the stock block temporarily without having to mod the lower. Not sure why HDPS didn't make them that way anyway.
AFAIK, there are 2 modifications to the UMP lower to mate to the stock block B: the chamfered cuts on the lower and the removal of the nub.

Click for full-size pics.

UMP lower with stock block B. Note the chamfered cuts circled in Red.


Chamfered cuts in the lower to mate to the stock block B.


The nub is removed and sanded down dfrom the lower.


Another look at the removed nub.
 

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Btw, AviatorDave did an exceptional job on the remarking the selector on my Navy UMP lower. Well, actually, there was no remarking. He took the UMP selector and made it fit the USC internals. This is exactly how I wanted my selector to look like.

 

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Is that possible without destroying the stock block?
It would still work fine without the little bump. It only holds the rear block from sliding off when the lower is removed. None of the changes needed to use a stock block would make the lower unuseable for a grafted type conversion.
 

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I've already trimmed the nub and rounded the corners for you. The nub merely holds the rear buffer on while the lower is out of the gun. It is a non-functional feature.

With the stock-block, you do not use the disassembly safety but I will include it in a baggie so if you ever get the fuse conversion, you can install it into the lower. It is a non-functional part other that prevents you from accidentally dropping down the lower with the bolt back causing the recoil rod to shoot out the back of the gun or into the stock cavity. HK really thought of everything.

I went ahead and began to remark the selectors. I know it wasn't part of the original deal, but I really want your conversion project to be as clean and as easy as possible.
 

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Discussion Starter #12
I've already trimmed the nub and rounded the corners for you. The nub merely holds the rear buffer on while the lower is out of the gun. It is a non-functional feature.

With the stock-block, you do not use the disassembly safety but I will include it in a baggie so if you ever get the fuse conversion, you can install it into the lower. It is a non-functional part other that prevents you from accidentally dropping down the lower with the bolt back causing the recoil rod to shoot out the back of the gun or into the stock cavity. HK really thought of everything.

I went ahead and began to remark the selectors. I know it wasn't part of the original deal, but I really want your conversion project to be as clean and as easy as possible.
I really do appreciate all that joe. Can't wait to get her in. I'll text you the tracking number tomorrow. Probably be around lunch time.
 

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Discussion Starter #13
So here's another question because I may be getting confused. The lower actually has the buffer in it correct? Is that what gets cut off?? Here's a pic I stole from hkparts.



I don't see the little backplate piece thing on the pics above. Does that whole thing get cut off?
 

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The backplate slides off the back. It's that part that's sticking up at the rear. There is a small nub that keeps if from sliding off while the lower is out of the gun. It really doesnt fall pff that easily but in true HK fashion, it eliminates any chance of loss. Thats what gets cut off as HDPS does not machine clearance in the block for it. I'll also be including the backplate and an extra buffer for the HDPS block as they do not come with them.

You only use the backplate and disassembly safety catch if you get the fuse conversion done.
 

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Discussion Starter #15
Oh!!!! Lightbulb. I thought the back plate had to be cutoff and the lower forever modified. That makes sense now.
 

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Discussion Starter #17
Does anybody know why stock blocks are made by hdps insted of hk?
Because HK doesn't care to convert a USC to a UMP. Thats why they make the UMP.
 
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