[Cr0nik]

Thanks, I'll try prying the contacts open a bit more.
I already tried flipping the return spring to no effect, but maybe if the contacts are a bit wider it might work.

I'll report back later when I get a chance.

Update

No fix but I see what you're saying.

I tried swapping different combinations of cutoff levers, trigger trolleys and triggers from among my spares to see how they meshed. You're right, the tolerances of the parts are all slightly different. I managed to get it working normally on auto. On semi it will cycle once; the cutoff lever will reset the trolley but then the trigger reset fails, it gets caught under the trolley like 1mm short of a full reset, and just locks the gun completely.

I'll keep trying different combinations. It's just weird because the working combination which came installed in this new gearbox shell just isn't working anymore.