Anyone with a full size .45 USP

[Gnome]

Maybe you're shooting with one or both of your thumbs on the slide release?

I used to have that problem with my Beretta 92. Supossedly, it's common with people with large hands.

[SchooBaka]

If you have a few magazines, next time you're at the range, use a felt marker to mark any mags used when the slide doesn't lock back on the last shot. See if this is repeatable with other reloads of that magazine. If so, the culprit is the mag spring.

I had this happen with a few USPf mag springs. Replace them with the +10% Wolf magazine springs. This is a common issue with these magazines. Oddly, my P2000sk using USP Compact 10-round magazines work very nicely with stock springs.

Even HK personal will (quietly, without witnesses) admit to using Wolf springs on their personal USPf handguns.

This makes sense. I've got a mag that will do that from time to time. Seems to fix it for a while after cleaning it, but it doesnt seem to take much for it to get dirty and start sticking again.

[Sig357]

If you have a few magazines, next time you're at the range, use a felt marker to mark any mags used when the slide doesn't lock back on the last shot. See if this is repeatable with other reloads of that magazine. If so, the culprit is the mag spring.

I had this happen with a few USPf mag springs. Replace them with the +10% Wolf magazine springs. This is a common issue with these magazines. Oddly, my P2000sk using USP Compact 10-round magazines work very nicely with stock springs.

Even HK personal will (quietly, without witnesses) admit to using Wolf springs on their personal USPf handguns.

+1 on this one. The mag follower pushes up on the slide catch. I purchased a HK Usp from a Calgunner that had the mags loaded with 10 rounds for quite some time. This made the springs weak and the pistol failed to stay open. With my new mags it worked great. My temp fix was to take the mag apart and slightly stretch the spring. This took care of the problem for now. I will look into Wolf springs though.

[Josh]

if i had to guess without seeing you shoot or inspecting the gun.

You are either not holding the gun firm enough while firing (limp wristing) or the mag springs are weak.

Normally if the gun will lock back on the mag when you manually retract the slide there should be no issues while firing.

The +10 wolf springs will solve that problem but they cause others. The USP .45 mags have a tendency to crack at the back weld near the top and the extra power wolf springs will accelerate this problem. I would just buy regular springs from wolf since its either pay a few dollars for a spring every once in a while or pay +$40 every once in a while to replace the whole mag.

Also just an FYI, springs do not wear out from time. Its all about the number of cycles its been through. You can keep them loaded as long as you want.