I recently purchased a used M17 Manual Safety from an individual local to me. I have a question about the P320 platform.

I've had a few situations where the M17 hand cycles fine with snap caps, but, if I pull the trigger on a snap cap the slide is a real bear to extract/eject the snap cap. The barrel moves down out of the locked position, but it seems the rearward movement is really tough. When this was happening I tried two different types of snap caps, A-Zoom and B's Dry File Snap Caps with the same behavior.

I now am not having this issue and the pistol hand cycles with and with out pulling the trigger as I would expect.

I've had the slide off and on a couple of times trying to diagnose what the 'issue' was. Did I do something correctly this time and was doing something incorrectly before? Anything you can suggest I look at before actually taking the M17 to the range?

Was the difficulty in cycling the slide that starting it to move was hard, but then it freed up?

All I can think of as a problem that existed only temporarily with two different kinds of snap caps is that there was something in the chamber that caused the caps to bind in place, but somehow that got cleared. The fact that the problem was worse or only occurred after pulling the trigger could have been due to the snap caps’ being driven into the obstruction by the firing pin. (Assuming I understood your description of the problem correctly.)

The downward unlocking of the barrel was OK, the inability to move was the slide in a reward motion. During my diagnosis I ran a snake through the barrel too.

Yes, that is what is mystifying to myself also as to why 'unfired' rounds cycled smoothly and without resistance. Only those where the trigger was pulled were ones that required a vast amount of force to extract/eject. My fear was like something binding in the striker assembly.