KWA USP hammer not always staying back
 

I got a used USP on the boards quite some time ago at this point. Right out of the box the trigger snapped which was quite a feat for me to replace. Literally 1 mag after getting the gun back together the slide catch snapped. I've yet to replace that but it's trivial.

Anyway since day one I've had issues with the hammer not always staying back when manually cocked. I've yet to actually take it to a game so I haven't put many rounds through it. The few times I've plinked the hammer seems to stay back when cycling with gas and BBs. when I pull the slide back it also seems to be hit and miss. It also seems that if the hammer is locked back and I pull it back a bit further sometimes it will release.

When I was doing the trigger replace I took a look at all the parts to see if anything had obvious wear that could cause it not to catch all the time. I couldn't find anything obvious but I also really don't know what I'm doing.

Any ideas?

So I've had this thing sitting in the box since I last posted this. Decided to take it out and have a look. I totally stripped it and put it back together in the hopes of figuring it out. Still can't find the problem. Thought I'd bump this back up and see if perhaps someone has any ideas.

If it's used there's a good chance the Sears inside the hammer we're worn to begin with.

Replace the whole hammer assembly and pray?

Those KWAs were based on the KSCs that came before and they're a few evolutions behind what a current gas gun would be. On the old gas guns it was all very much about looking good vs. actual function.

In any case like this I've found the best solution is to buy a new gun, use that as the mule/backup/yardstick while repairing the first gun, and then sell one or the other when it's all working.

Is it a NS2 System USP or the (older) Hardkick System USP?

Either one have a hammer assembly that is a huge pain to take out from the gun or to put it back. It is not like the Marui Glocks which you can replace the whole hammer assembly easily. To replace pretty much anything from the hammer assembly of a KWA/KSC USP you have to take almost everything out, and it is not simple.

I have some experience messing around with it and I have a scavenged (and working) NS2 System USP that can be used as a parts donor gun, for a same system (NS2) USP. If your want to try repair it yourself, there is some KWA USP disassembly videos out there, and if you run into specific problems such as some parts stuck, I can help you here, too. But if you want to save yourself some pain I should be able to do the work for you as well (I am relatively close to your area and I occasionally travel to Guelph). Also if you are interested in the parts donor gun you can PM me.