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Discussion Starter #1
I have a USC/UMP conversion using an HDPS short barrel and I was wondering if anyone may have an idea about a problem I'm having. I've put about 300 rounds through the gun, and have already had about 7 failure to feeds.

The rounds are being stripped from the mag, but then they get pinched "nose up" between the bolt group, and the barrel's feed ramp...and never make it into the chamber.

I didn't know if anyone else has had this problem with a non-factory Hk UMP barrel and I am just looking for any advice anyone could possibly give.

Thanks for any input!

-Mike
 

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Sounds like a problem with the fit of the lower receiver.
I had a UMP lower that had to much material taken out of the front hooks, and had the exact same problem.
 

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Not that I'm any expert on USC/UMP's but have you tried another magazine or pulled the mag apart for cleaning and inspection? Tried different ammo?

I'm in the middle of building my own USC/UMP and a little play in the hooks doesn't appear to affect alignment so much it would cause problems feeding.

I'm not saying extreme play couldn't but it would have to be so much play it affected the way the receiver hung and lined up etc.
 

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I had the same problem with my UMP, here's the thread I posted about it.

http://hkpro.com/forum/showthread.php?t=61183

The feed failure was inconsistent but the bolt hold-open catch was having a lot of problems. I shipped it back to Wade at Top-Notch who swapped a few springs in the lower and test-fired it and had no problems. I have since not had any problems.

I think the second poster in the thread said something about positioning of the lower, that would be my guess.
 

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Discussion Starter #6
Thanks for the responses guys. The lower hooks are done just right, and the lower to upper fit is nice and tight...no play at all so I don't think that could be it. I have four magazines and have only used two of them so far...so it is possible that it is one of the magazines. I'll start keeping track of any more FTF's and see if they keep happening while using one particular mag. Hopefully that is the case.


Thanks again!

-Mike
 

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Thanks for the responses guys. The lower hooks are done just right, and the lower to upper fit is nice and tight...no play at all so I don't think that could be it. -Mike

I've seen too tight be more of a problem than too loose. If the hooks aren't cut right and they bind, it puts a twist on the lower. Most problems I've seen are inconsistent machining- the one hook is cut differently than the other- this cocks the lower.

Since you have the aftermarket barrel, swap in the original and see if it goes away.
 
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