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Discussion Starter #1
Some of you may know I purchased a USP parts kit with a black slide to complement my stainless USP 40 (http://hkpro.com/forum/showthread.php?t=70712). The black (Hostile Environment) slide is date code KE, while my stainless is date code KH. It was my assumption that the changes in the older USPs, and the newer USPs were mostly small changes that didn't really effect function between the two generations. But it turns out one of those small changes doesn't allow the swapping of a KE date code slide with a KH date code slide.

I knew that the firing pins were different, the catch/control lever assembly was different, the hammer was different, the mag release was different, and that the lettering on the sides of the slide was different. I didn't know that the slides were different, and that the disconnector was also changed. As a result, I tried to put an early generation HE slide onto my later generation frame. It ended up not firing. A pull of the trigger on double action resulted in a short, light trigger pull that moved the hammer about a quarter of an inch rearword and then dropped it back to the half cocked position. On single action, the hammer remained cocked when the trigger was pulled.

So I pulled the HE slide off to compare it side by side to my stainless to see just what was different. The only interior difference can be seen below.



As can be seen to the top left of the two slides, the stainless has a much larger machined area than the black slide. So, the black slide was pushing down the disconnector, causing the trigger to be disconnected.

Well, at least I didn't break something. But obviously, it left me scratching my head as to what I could do to fix the problem.

When I got home, I compared the disconnectors from a KE date code gun to the disconnector in my KH gun. Below are the two. The KH is on the left, KE on the right.



As you can see, the KH (left side) disconnector has a greater length on the top of it than the KE (right side) disconnector.

Placed on top of each other:



The holes all align, and the KH (bottom) disconnector is only bigger to what would be the rear of the gun.

So it seemed logical to me that a simple swap of the disconnectors would fix the problem. I just completed the swap, and everything seems good. I don't see why the design changed like it did.

Did they have a problem with disconnectors breaking back with the early generation USPs? It seems like this design change only added strength to the disconnector, but added more machining to the USP slide. What gives?

I'm not going to be using this as a self defense gun until I test all this out. But the hammer lifts and drops properly in double action, it cocks, hammer drops right in single action. Hammer remains cocked when you pull the trigger, hold the trigger rearward, and cycle the slide. Everything appears to be a go.
 

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Very nice write up Mav. My .40 S&W HE conversion slide for my stainless USPc 9mm is still running like a champ. Glad to see things are working out for your swap.
 

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Discussion Starter #3
Glad to see things are working out for your swap.
I hope it works out. I can't get to the range to test it out until I get back home, so I have to resort to the P2000sk for home defense for now :(

Only 4 more days until I can test it...
 

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Thanks for the report Maverick.

I have a KE dated USP9 so this is most useful information for me.
[making notes]...[done]

Thanks, :D
Miku
 

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I hope it works out. I can't get to the range to test it out until I get back home, so I have to resort to the P2000sk for home defense for now :(

Only 4 more days until I can test it...
Ah, I guess I was lucky then that both my USPc 9 and the USPc 40 slide I picked up from you were dated KI. So it appears there is some method to HK's madness when dating their parts, other than for identification purposes. :6200:
 

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Discussion Starter #6
Just did a little search for "disconnector broke" and found this thread:

http://hkpro.com/forum/showthread.php?t=6202&highlight=disconnector+broke

So there you have it. They beefed up the disconnector to prevent that breakage.

IronChef, I wonder if the USPc had any of these changes... it might have been produced after all the hammer box revisions. So the earliest USPc slide may still work on the newest USPc frame. Just a thought :)
 

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Discussion Starter #7
Finally got to test the old disconnector inside the "new" frame and on the newer slide. No function problems whatsoever with either the KE or the KH dated slides.

Bonus.
 
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