I have a M&P 9 FS with the thumb safety. I also have an M&P 40 FS without the thumb safety. Is it possible to put the 40 slide and barrel assembly on the 9 frame so that I have a 40 with a thumb safety? Thank you guys for any advise you may have!

I wish you'd have gotten an answer to this question. I am curious myself. I have two compacts of different calibers, one with the thumb safety, one without. I have swapped the slides and everything seems to work. I haven't fired them with the slides swapped. Just need to know that it is safe.

Out
West

as far as i know the lower polymers are completely identical, aside from the safety of coarse. Every after market part is made for both the 9 and 40.

Switch them and rack them (empty). if they look identical and rack as usual..

Or you could just email S&W