I have seen differing opinion online. Some say only 40SW can be converted to shoot 9mm but not vice-versa.

With Lone Wolf slide and barrel kits, can the 17 safely shoot 40SW and 357SIG?

I have converted a g17 into a .40 or put on a g22 slide and after market .40 match barrel with no issues. The way I see it is... most likely they are not going to sell dangerous or exploding firearms well at least not from reputable manufacturer.  Jmho

From what ive read, they want to tell you you can convert down in caliber, not up. Idk i the 9mm slides are not as thick as the 40s&w ones. But thats usually the easy to do is convert down. Like the previous post mentioned he put a whole 40s&w slide one. Thats more then a 130 dollar barrel. I know that the 45acp and 10mm barrels wont fit cause their slides are much bigger. As for the sig idk. Only option i would suggest is 22lr which advantage arms makes a kit, tactical solutions makes one also. But this kit replaces the whole slide and mag change and your done. I own an advantage arms kit, but did not run any rounds through it so far. Thing to know about 22lr conversions is that they are picky on what types of ammo it works with. Hope that helps a bit. lol