New KJ P14-45 problem involving underpowered shots

[Captain Tenneal]

Seems like the old problem was a simple valve sticking problem (lots of lube solved that problem) but there seems to be a new problem with my P14.45.

Every so often whenever i'm firing it, instead of having a rather straight and hard trajectory (like it's supposed to) it just pops out and goes about five feet before hitting the floor. The slide cycles and the only noticable change is that the timbre of the sound of the gun when it goes off goes down, and that the stench of propane seems to be intensely strong, nevertheless I think i'm still getting about the same mag capacity/preformance as I did when they all worked fine.

I've handloaded single bbs into the chamber and fired them, and the problem happens every so often. Plus I'm using three new KJ mags and one old one and they all seem to have this problem, and it's not consistant at all. No pattern in the underpowered shots as far as I've seen, so I'll assume it's the gun itself not the mags.

Any help would be appreciated.
Thanks in advance.