Fnx40 to 9mm barrel swop using oem barrel

Hey there everyone, I'm new here and I had a question for y'all.

I know with sigs for example the sp2022 you could change a 40cal to 9mm by swopping barrels only (some say recoil spring to and obviously the mags)

With a 40cal to 9mm you can do the swap because the breach face is big.. however if you try to do it from a 9mm to a 40 that will not fly.. that might be where a conversion barrel would come in..

Now I know you can use a conversion barrel and they sell them for the fnp and fnx.. however I can get a perfectly good oem 9mm barrel muuch cheaper..

So I was hoping if someone who knows alot about different calibers and breachfaces would be able to tell me..

I would think it would work.. as good as a conversion barrel.. or as good as using a 9mm slide with a 9mm barrel? Probably and obviously not I'd think it might expel more gas and maybe loose a little speed would it fire ? I'd guess so..

However I wanted to hear if someone every did it?

Orrr from someone who is like a genius who knows this stuff very well..

Thanks so much, I hope to hear from you soon.