I seem to be having the same issue with my P+ 16340. It doesn't fire with most of my atties. I've tried Spheroid, Ti Bliss, Nahual etc. Some of these have adjustable positive pin, which can be made to protrude more from the bottom connector, but not all. It fires fine with 510 atties, which have a positive post that sticks out quiet a bit. I think the positive post in the P+ sits pretty low and isn't making contact. Is there any way to raise the positive post in the top cap? Any suggestions?