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Discussion Starter · #1 ·
I have a USPF9mm, datecode KD, and I want to replace the flat sear spring with a nickel plated sear spring. However, upon removing the old stock spring , I noticed a huge difference in the shape of the two springs. The old spring is shaped so that it clamps to the frame differently than the new style spring. The new spring will fit, but there isn't a way for the middle leg of the spring to fit securely like it would on my new USPF45. Does the KD model need to be altered in some fashion so the new style spring will fit securely?
I like the old gun and have updated all the parts and installed the Match Trigger setup, but I want to be sure the new style sear spring won't "pop out" at an inopportune time.
 

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I worked on a USP 9mm KD (1993) gun which I believe was was the first year for USP. That gun had some significant differences compared to later USPs.

I remember there being something very different (compared to the later and much more common design) about that flat spring and/or how it's held in place by the frame. I am fairly sure the upgraded (shiny) flat spring is not intended to go into that gun (the KD 9mm USP design). I know when I worked on it, it was not intended to. But maybe there is a more recent version of that shiny flat spring. I doubt it, but maybe.

If I remember correctly, the newer spring will not stay in the gun. As Tracker01 noticed, it will fall out (and it did for me when I shot it). I believe one way to fix this problem was to somehow use the tip of a soldering iron to make a minor, but permanent, modification to that part of the frame (where the flat spring goes). I think that is a bad idea and I never did that.

If I remember correctly, I had trouble reinstalling the original flat spring. What worked for me was to make a very small "L" shaped tool by bending the tip of a pin 90 degrees. With the flat spring out of the gun, I positioned the tool on the flat spring to hold the middle section up/out. Then I slid both into the gun into the final position for the flat spring, and then removed the tool.

I am going off of my memory of events many years ago. So I could have some of this wrong and I may have left out something important. But I hope this helps.

Tracker01, if you want, I can look into this further and possibly check my notes. But it may take a few days to get back to you.

Joe Mamma
 

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Discussion Starter · #4 ·
Thanks for your response Joe Mamma, everyone I've asked is sure that I've lost my mind. Your memory serves you well, the flat sear spring is very different, hence the new style spring will not stay in the gun when fired. Your suggestion of using a soldering iron to remedy the situation is a distinct possibility. At least should be explored. Thanks again for the response.
 

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That part of the frame is taller than the updated models, or maybe it's more correct to say that the bottom cut of the spring attachment shelf is lower the grip frame. When you try to slide the sear spring into place, there is too much material going lower, preventing the middle 'leg' of the sear spring from clipping into place. Hk can remove the extra material for you. This is at least part of the reason why match trigger kits aren't compatible with KD date codes.

"Aren't initially compataible, but the can be updated to accept the MTK"
 

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That part of the frame is taller than the updated models, or maybe it's more correct to say that the bottom cut of the spring attachment shelf is lower the grip frame. When you try to slide the sear spring into place, there is too much material going lower, preventing the middle 'leg' of the sear spring from clipping into place. Hk can remove the extra material for you. This is at least part of the reason why match trigger kits aren't compatible with KD date codes.

"Aren't initially compataible, but the can be updated to accept the MTK"
I'm not sure if I completely agree with all of this. If I remember correctly from many years ago when I installed a match trigger kit in a "KD" date code gun. I used the original flat spring (not the new shiny one), the match trigger kit (except for the shiny flat spring), and 2 or 3 extra parts (which were needed because of the older "KD" design).

The trigger feel improved significantly, and the gun was reliable for many thousands of rounds afterwards.

So I do not think it is absolutely necessary to remove any material from the frame.

I'm not trying to argue with anyone. I'm just trying to offer some additional information.

Joe Mamma
 

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So I do not think it is absolutely necessary to remove any material from the frame.
No worries @Joe Mamma. That is true. You could go without the nickel plated sear spring. There are other problems with getting the complete match trigger kit installed on the KD date codes but I'll defer to TooSixy on all the specifics. If I remember correctly the control latch & catch are one solid/mated piece on the KD's and the more recent design is a 2-piece operation.
 

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I am new to HK's but have been a gun tinkerer for more than 40 years. I asked HK parts if the match sear spring would work in USP date code KD, they said it would. Have learned what to do myself and what to have done by a pro. I had the match sear spring installed by a HK armorer and the gun works and shoots just fine
 
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