FTF on first strike with HK USP

[Deavis]

I posted a while back on some issues I was having with an HK USP 40 that wouldn't always light off primers on the first strike from a cocked position. Usually a second pull of the trigger in DA mode lit off the round. I switched from CCI primers to Winchester and haven't had an issue in 1-1/2 years... until now!

The thing is that the gun will light 200 rounds and then I start with a different load I made a little while back and they start misfiring. I've checked the loads and the primers are all seated within spec before firing and there seems to be no pattern as to when it doesn't light (different brass, similiar depth, etc.) The gun can be freshly cleaned or filthy, it doesn't matter I can get misfires in either state. I think that the gun is marginal and the batch of primers might be a little bit harder than normal and my gun just doesn't have the oomph to light them off.

I sent the gun in to be serviced by HK and they replaced the hammer spring. Obviously that didn't solve the issue. I'm thinking about replacing the hammer spring with a 16lb wolff spring to see if that helps. Can anyone think of something else that could be causing this issue? I thought about replacing the firing pin spring, but I'm not sure that would help or not.

Also, the same loads that my gun misfires on works fine in a friend's USP 40. As a matter of fact, all the parameters from his gun are better than mine, i.e. better SD, ES, etc! His is much newer than mine but it makes me wonder if weak ignition is causing the parameters to skew a bit. Mine is a much older model than his and has the smaller hammer of earlier models.

Any ideas would be appreciated.

 

[mpthole]

Two years ago I was having light primer strikes with my USP .45C on both reloads and factory ammo. I sent it back to HK. When I got it back it had a note that said the gun was so dry on the inside that all it needed was a little lube. He asked what I had been using to clean it and I told him Gun Scrubber. He said that was fine, just don't hose out the inside of the gun so much. Ooops.

That was my experience anyway... haven't had a failure since.

Total turn-around time was maybe 1 month...? I thought their customer service was pretty good. Way better than Colt's - they had one of my rifles for almost 4 months and when I got it back all the note said was 'test fired - ok'.

 

[Jim K]

I second the advice on lubrication, but also advise a check of both firing pin protrusion and headspace. If the firing pin won't quite reach the primer for either reason, you will have misfires and they may be mostly with a specific brand of primer.

A heavier mainspring might help, but of course will make the DA pull heavier.

Jim

 

[Deavis]

all it needed was a little lube.

I'm lubing it where the manual says, where specifically did you apply the lube to fix the problem. I checked the firing pin protrusion and there seems to be ample protrusion with a case held by the extractor against the breech face. I can't press it all the way out. I guess I'll clean out the firing pin hole a bit, replace that spring, and then replace the main spring as well. I'm not really concerned about the DA pull... It will just make my hands stronger

 

[pbhome71]

Did you get a light strike, or there was no strike? If you get no-strike, it might be a timing issue that I have seen in my USP.

My USP 40 has a timing problem when I pull the trigger slowly. This happens with both DA, and SA. I can reproduce this at will. Here is what I found, when I pull the trigger slowly, instead of releasing the hammer to strike the firing-pin, the hammer block got release first. Instead of the hammer strikes the firing-pin, it strikes the hammer block which prevents the hammer to strike the firing pin.

If I pull it fast, it works everytimes.

My 2 cents.

-Pat

 

[mpthole]

where specifically did you apply the lube to fix the problem.

HK lubed it when I sent it back. The only place "extra" I now put some lube is on the mainspring - and I don't hose down the frame with gun scrubber anymore either. I guess occasionally I'll put a drop where the hammer connects, rub it around a bit with my finger or a q-tip; and then once its reassembled, cycle the slide and drop the hammer a few times to get it worked in.

 

[Onmilo]

Instead of the hammer spring, check and replace the firing pin spring.
Too heavy a firing pin spring in any firearm can cause repeated misfires.
Also check the firing spring tunnel and see if a burr or impacted goo is limiting the firing pin free travel.
Next check to see if the slide is not going completely into battery on the first round.
Are you riding the slide down with your hand when you chamber the first round?
Pull it back and let it go, you aren't going to break anything doing this.

 

[Deavis]

Guys, thanks for the tips.

pbhome71: it is always a light strike, never a no-strike. I've been practicing double taps and it will FTF. When I chrono slowly, it will FTF. Everytime, when I eject the round, there is a light mark on the primer.

mpthole: sounds like what I am doing currently. I'll give it a real thorough lubing when I replace the mainspring and firing pin spring.

Onmilo: I'll make sure and clean out the firing pin hole and check the pin for any damage. I've ordered a new firing pin spring from Wolff and will replace it first before I change the mainspring out. This does not seem to be a battery issue as it can happen anywhere during the course of a magazine. As I mentioned, it hasn't happened for 1-1/2 years and the only thing different is I am using a load I made a little while back. Hence my thought on the harder cup and my pin strike being marginal.

The springs are shipping today so hopefully I'll have some results in a couple weeks.

 

[Deavis]

Finally got the springs in from Wolff. I took the firing pin out and gave it a thorough cleaning and then cleaned out the pin hole really well. Replaced the firing pin spring with the new Wolff spring and reinstalled everything. I didn't notice too much gunky particulate when I cleaned it but it was definitely dirty inside the main firing pin hole after all the shooting I've done with it.

Gun lit off the problem ammo without any issues so it looks like the problem has been solved without changing the hammer spring at all.

Thanks for the help guys.

 

[mpthole]

Deavis - glad to hear your HK is working better! I've never taken mine any further down than field stripping for cleaning. Did you have some directions to go by? Just curious because I don't know if I trust myself to take down my HK... 1911s are another story - no problem with those, but HKs kind of scare me that way.

 

[Deavis]

mpthole - I used the instructions posted over at hk pro from Dr. Kiljoy This site put it together nicely.

http://www.brandywineits.com/HK/index.htm

Honestly, the only pain was keeping the firing pin in place because it is held by the firing pin block saftey but just short of where it needs to be so you can drive a roll-pin through. If you slightly move the pin without securing it, it flies right out the back and the block pops out as well.