9x18, impossible. The bore is actually a good deal fatter, they flat out won't fit. They're like 9.2mm or something funky
. They're commie-derived, waddya expect?
9x17, bad idea but if the gun uses moon clips, possible in a pinch.
But here's the problem: MOST 9mm revolvers that use moon clips also have the cylinder bores cut internally so that there's a "lip" at the case depth, similar to what's down the barrel of a semi-auto. That way, you can load and fire rounds without a moon clip, you just can't quickly extract: you have to open the cylinder and push each round clear with a pencil, cleaning rod or similar.
Well when shooting 9x17 (aka: 380ACP/9mmKurtz), two millimeters into it's travel the round will hit that "ledge", potentially warping the bullet, putting stress on the cylinder, God knows what else.
THAT SAID: if I had a 9mm wheelgun, some moon clips, some 380 ammo and I needed to defend myself, I'd stuff 'em in there so fast it'd make somebody's head spin
.
But it's NOT safe. OK?
Last point: if you MUST have a 9mm gun that shoots both, any machinist can shave that "ledge" to an "internal forcing cone" rendering the gun safe for both calibers. It would then be a moonclip-only proposition in 9mm.
If he was really clever and the gun was known to be tough enough, he could bore that "internal forcing cone" deep enough so that it could shoot 9x23, 9x21, 9x19 and 9x17 all in the same gun, all with the same moonclips. As one example, any 9mm DA revolver that's known to be tough enough for 357 could do this safely, such as the SP101/9mm and the old Security/Service Six series done in 9mm.
With Taurus' 5-shot 9mm snubbies, I would compare the dimensions to a similar Taurus 357, make sure the star/ratchet is the same, then Rockwell test critical areas, make sure they're the same. They *probably* are but don't trust a KB to "probably".
NOTE: if doing this, accuracy will get worse the longer you "freebore" (float a bullet down a cylinder bore that's too fat). So 9x17 in a 9x23 chamber with no "ledge" will be safe, but accuracy may be poor. Ditto 9x19. So if you want peak accuracy in 9x19, leave the chamber that length. Removing the lip for safety with 9x17 won't be an accuracy problem for the 9x19, or at least not much of one.