I bought an H&K USP 9mm (old model, no hex barrel rifling or PRK-approved safety) and for some reason once every 50 rounds or so I'll pull the trigger, the hammer will fall and the gun won't fire. I'll check the ammo and the primer is dented slightly. If I pull the trigger again (double action) it'll fire just fine. What could cause the firing pin to fall and dent the primer but not with enough force to fire the gun?

Thanks,
Jason Abels

Ohhh oh, I know what it is.  Clean out the firing pin channel.  They do that when it hasnt been cleaned out in forever.  Spray it out with gun scrubber and the problem with dissapear.  Also be sure to use synthetic lube.

What kind of ammo?  Could be hard primers.

Agree with schapman43.  I finally got around to taking my firing pin out and cleaning it after my USP Tactical started to do the same thing.  So the firing pin needs to be removed and cleaned every two thousand rounds or so for maximum reliability.

Good deal, thanks guys. One last question, how do I remove the firing pin? Do I have to knock both of those retaining pins out of the top of the slide or just one?

Thanks,
Jason