Strange problem with USP

[JKrew]

Last year I bought a used police trade in USP 9mm. I took it out shooting for a little to test it and din't notice any issues. I just took it out again last week and sometimes the hammer stays back as if it is single action, and sometimes the hammer goes back forward as if it is double action only. It was completely random. I have not taken it apart beyond what HK recommends for cleaning. Has anyone ever experienced something like this before? Would it be best to just send it to HK to have them fix it?

 

[BradMacc82]

Send it in to HK, life is just easier going that route. Safer too.

Haven't had that issue with my USP so far.

 

[amoebicmagician]

does it have the LEM trigger?

 

[Blaster229]

does it have the LEM trigger?

Bingo.

 

[BradMacc82]

Is that an issue with the LEM's?

Only have experience with the Match trigger, so that's a new one to me.

 

[JKrew]

I thought it was LEM, but something is wrong since it randomly goes between SA and DA. The DA is lighter like the LEM trigger would be.

I have another USP with a V1 trigger so I know how a normal one should feel.

 

[coopermania]

H & K LEM Trigger

The HK LEM is basically artifice. It uses a two-piece hammer, one part internal and one part external. When the slide is racked (loading the gun or during the firing cycle), the mainspring is compressed and kept in place as with any single action mechanism. However, the external part of the hammer moves fully forward and so does the trigger. In essence you have a cocked pistol that doesn’t look cocked.

The first shot is long like a traditional double action pull, but it’s not any heavier than subsequent trigger pulls. The reset is certainly longer than most striker-fired guns or a 1911, but it’s only about a third of the total trigger travel arc. Three different configurations are available:

V1: nominal 4.5# trigger pull; uses standard trigger return spring and standard firing pin block spring … this is essentially the standard P30 SA trigger pull from the DA/SA variant

V2: nominal 7.3# trigger pull; uses extra strength trigger return spring and extra strength firing pin block spring … the one example I have measured 7# 10oz out of the box and has dropped to 7# 8oz after 1,000 rounds

V4: nominal 6.1# trigger pull; uses the extra strength trigger return spring but a standard firing pin block spring … for reasons explained below, I believe this is probably the best option

The one I’m most familiar with is the V4. The extra strength trigger return spring plays a tremendous role in counteracting the long reset. Obviously, it’s the speed at which you manipulate the trigger rather than simply the distance which determines how fast your next shot will discharge. While moving a longer distance would seem slower, the stronger trigger return spring literally slams the trigger to the reset point faster than you could move your finger alone. Will it be as fast for blind “for the fun of it” rapid fire? Probably not. But I was pulling .20 splits give or take a couple hundredths after just a few boxes of ammo.

The extra power firing pin block spring serves no purpose but to increase the trigger pull weight, so I’m planning on replacing mine with the lighter one to get about a 6# trigger pull, which I find is close to ideal for a practical gun.

 

[Pinecone]

Hmm, sounds like the Daewoo Fast Action.

Single action, cocked and locked, but with the hammer down. Trigger pulls cams hammer back against a VERY light spring pressure, then final pull releases hammer, with a normal SA force.

 

[DocAitch]

I have a CZ 82 that does the same-on some shots the hammer follows the slide down and then it fires DA. It has never doubled.
I suspect a problem with the sear, but am not a mechanic enough to figure it out. I do have plans to pull it apart and look at the sear for abnormal wear.
I don't really feel like sending a $250 pistol back to CZ with the expense and hassle.
My other 82 runs perfectly.
DocAitch

 

[Pinecone]

If the hammer is following the slide down, take it a proper gunsmith, or send it to CZ for repair. That is a VERY dangerous situation.

Both from a handling standpoint (doubling or full auto) and a legal standpoint (BATFE could arrest you for an unlicensed machine gun).

 

[coopermania]

If the hammer is following the slide down, take it a proper gunsmith, or send it to CZ for repair. That is a VERY dangerous situation.

Both from a handling standpoint (doubling or full auto) and a legal standpoint (BATFE could arrest you for an unlicensed machine gun).

I believe the good Doc has a handle on what needs to be done with his pistol, I don't believe ATF will get involved with a pistol that the hammer that follows the slide.
Gotta love you guys that feel the constant need to add the ATF gloom and doom to posts for something that just is not there.
Coop

 

[OrbitalEllipses]

But it's an unregistered machine gun!

 

[Pinecone]

I believe the good Doc has a handle on what needs to be done with his pistol, I don't believe ATF will get involved with a pistol that the hammer that follows the slide.
Gotta love you guys that feel the constant need to add the ATF gloom and doom to posts for something that just is not there.
Coop

Do some searching about the BATFE abuses regarding full auto.

You may not be scared, but I am. They have done some STRANGE stuff.

Including modifying the firearm, then when it doubled, charging the person with an unregistered machine gun. Huh???? You modify it, it is not in the condition when I had it.

 

[coopermania]

Like I said your adding issues to a firearm that just are not there.

 

[smokey]

How are you holding it? Are you positive you're not decocking it under recoil?

edit...nvm, saw you have another one to compare it to.

 

[amoebicmagician]

what?

He only has the one USP, and the LEM does not have a decocker, let alone a safety on the pistol, and if he was talking about his cz-82s, the pistols do not have a decocker either, the hammer must be manually dropped each time you want to proceed from double action.

 

[amoebicmagician]

the thing about the lem trigger is that the visible part of the hammer exactly corresponds to the trigger's position, so if you keep the trigger depressed after firing, the hammer will seem to be in single action mode, is this the issue you are having?

If the trigger pull is light either way, then your sear is fine.

 

[OrbitalEllipses]

what?

He only has the one USP, and the LEM does not have a decocker, let alone a safety on the pistol, and if he was talking about his cz-82s, the pistols do not have a decocker either, the hammer must be manually dropped each time you want to proceed from double action.

You can retain the safety while using LEM. Simply use the original V1 hammer axle and safety with the appropriate detent plate: No decock function, but safety is there.

 

[Corporal Doug]

Sounds like an LEM trigger. I loved my compact .40 with that. Double action only, with a heavy trigger that felt light. 3/4 of trigger travel is light, the last 1/4 is where all the weight is. I shoot great with it.