I have a P320 pistol that I have swapped back and forth with a variety of grip modules. Last time I swapped and reassembled, the pistol did not function. The slide was cycled and the trigger stops and no firing pin drop. I disassembled several times and insured the takedown lever and slide catch reengaged and still does not work. I have not tried to disassemble the FCU. Suggestions?

Is the slide the same, or swapping between slides? And you have locked the slide back with the slide catch? (I think that is what you meant above, just being sure.)

The Sig Guy has some excellent videos on the internal workings of the P320.



https://www.youtube.com/watch?v=D3vWyscrmCY

Here's his Youtube channel:

https://www.youtube.com/c/SigGuy/videos

A different video about a more likely issue.

https://www.youtube.com/watch?v=lfFpQ_0GQpY

Thanks for the replies. My problem was mismatched parts between the original FCU and the improved FCU. I now have an improved FCU with grip and an old style slide that is incompatible. Time to spend more money.