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Discussion Starter #1
I converted my USPc to LEM last week and everything felt fine. Like the LEM trigger. I retained the stock hammer spring because I felt the long one was WAY to heavy a pull on the long stroke. I had read that you can keep your old spring to get a lighter pull. I took her to the range today and she was hitting the primers way too light. Only popping off 1 round every 2 or 3 tried.

I assume a firing pin spring is in order (this guy: HK Spring | HK FPBS - HKPARTS.NET) but I wanted some clarity first.

She's a KG date code if that matters

tyia for compensating for my lack of hk education
 

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I retained the stock hammer spring because I felt the long one was WAY to heavy a pull on the long stroke.
The hammer spring is already compressed so your long trigger stroke is not working against the hammer spring at this point of the pull but rather the Trigger Rebound Spring.

I had read that you can keep your old spring to get a lighter pull.
This is true. It should be striking with roughly the same force that it was before. Remember that this was the same spring that was sending the hammer forward just fine with V1. The only real difference is the two part hammer but that shouldn't effect this.

I took her to the range today and she was hitting the primers way too light. Only popping off 1 round every 2 or 3 tried.
Something obviously doesn't sound right with this. Did you change anything else? What ammo are you using? One thing I would do is to remove the firing pin and make sure there's no greasy build up in the firing pin channel. Clean it out really well and refrain from oiling it when reinstalling as the oil will act as a dirt magnet. Personally I would strip the pistol and reinstall the LEM kit. Maybe something is out of kilter and a reinstall will get it right.

I assume a firing pin spring is in order (this guy: HK Spring | HK FPBS - HKPARTS.NET) but I wanted some clarity first.
You can change this if you want to but it's not going to make a difference as far as the light strikes go.
 

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HK notes they made the LEM hammer spring stronger for reliable primer ignition. That said I've had no failures to fire in either my HK45C or USP9C LEM pistols using the lighter, smoother V1 hammer spring.

-- Chuck
 

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Ditto on the V1. All my shooters have been switched over to LEM V1 and I also retained the original hammer spring in all of them. Never had a light strike yet. I agree that there is something else going on but changing out the hammer spring is fast and easy. A new hammer spring should have come with the LEM kit and it only takes seconds to change so give it a try. A firing pin spring though, as said, matters not a whit unless it is broken and binding the firing pin. Either something is binding your firing pin keeping it from moving freely or something else is installed incorrectly.

You didn't do something silly before changing over to the LEM did you? Something like putting in a Wolf 10 pound hammer spring in the old V1 to reduce trigger pull? If you did, get that darned thing out of there. The 10 pound spring barely has enough oomph to light off a primer in the standard V1, let alone the LEM. I've been down that 10 pound road and it caused a much reduced hammer fall in the USP and UPSCs in standard V1, but when I tried one in the LEM it was so slow in falling I did not bother to try and live fire it. Total recipe for failure IMO.
 

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Discussion Starter #5
thanks for all of the input. She was a V3 before I switched, I left the old hammer spring in there because I liked the feel of the long pull better. I will swap in the spring that came with it and give it a whirl.
 

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Discussion Starter #6
so I finally got around to taking her apart and took my time this time. I swapped the hammer spring with the short one with the kit and did the "pencil test". It launched it a few feet. I then switched out the new trigger i installed with the old one and that sucker sent the "pencil" about 6 feet. Me thinks the FP issue my be resolved. I note the long stroke is pretty heavy and the short stroke is very light. Have to run some drills to see if I am happy with her...well and that she fires properly ;-)

thanks for the help
 

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OK. So your USPc was a V3 before you switched. Did you mean to say V1, because V3 is a DA/SA with a decocker but no safety. Is that what you had?
The short hammer spring in the LEM kit is meant for the HK45c. The longer one is the one for your USPc. What trigger did you switch out? Did you mean the trigger rebound spring (TRS)?

If I understand you correctly, you're now using the hammer spring for the HK45c and the original V1 Trigger Rebound Spring?
 

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Discussion Starter #8 (Edited)
toosixty

Miine was a V3 (DA/SA with decocker only, no safety), from the USP website
Variant 3: 
Double action/single action without "SAFE” position. Control lever (decocking lever) on left side of frame.
I now have the short spring from the LEM kit (which is black in color and as I understand is for the HK45c) and the original TRS that came with it in the pistol. The long spring (more silver in color) which is supposed to be the one for my pistol needed a 'roid raging beast to pull the trigger. Honestly, it wouldn't work with the long spring. The original hammer spring that was in my USPc is actually shorter than the HK45c version that came with the kit.

When I did the "pencil test" with the TRS from the LEM kit and my original hammer spring the pencil went maybe 12". No wonder it would hit the primers hard enough. I swapped to the long hammer spring from the kit and there was no way to successfully cycle the weapon. So I decided to swap the TRS to the original one and work through all of the spring again. With the original TRS the original hammer spring sent the pen a few feet, maybe 2 or 3. The HK45c sent the spring about 6 feet which is about the same for my Glock and Colt Series 80. The long hammer spring, forget it. 90lb full stroke pull.
 

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Did you purchase the gun new or used? Was there any custom work done on that gun? It sounds as if the original hammer spring was modified (shortened) or replaced with a lighter one as Big Bore pointed out.

I have a couple of V1 USPc's and the only difference between my V1 and your V3 is the safety. I have Light LEM in all of USPc's (original TRS and hammer spring) and they work without any issues.
 

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Discussion Starter #10
I bought it used and I am still fairly new to HK (had a USPc and full in 40 but never modded them). I have no idea if any changes were made. I think I will hit the range today and try both the original hammer spring and the short hammer spring from the LEM kit to see how they perform.
 
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