[Mericet]

As others said; fit finish and add-ons for the most part. There will also be a difference in the feel of the trigger between the different factory guns. I have not had any (non-ammo) related problems with my Para double stack in .40S&W and I have not had issues with the one (basically a Nighthawk Custom frame and slide) I built for myself. Not that I have put a lot of rounds through it either.