Moon clips are a good thing if the clip is a good design.
The 9x18 basically, ballistically, is a .38 special +P. It' be a desirable revolver in an alloy design IMHO, something you can't do with the parabellum round except with expensive scandium or titanium.
However, would it sell? Moon clip revolvers seem not to be so popular. An odd caliber would flop, I reckon, worse than the 9x19s have.
As to the original question of ammo, I doubt you could possibly fire a rimmed standard cartridge in a moon clip caliber due to inadequate rim thickness. The .45 autorim has a very thick head to take up the space required for using the moon clips in a .45 ACP revolver. Even if the rim thickness were good, the .38 head spaces on the rim and I think it is longer than 18mm. A 9x18 revolver would have ridges in the cylinder chambers for it to headspace on the front of the rim. So, I say, NO, it wouldn't interchange, but that's pure speculation based on what I do know about the two cartridges.
According to my quick calculations, the 9x18 is .708" case length and my Speer #8 manual says the .38 S&W case length is .773", so the .38 case is longer than the Mak round, which means it wouldn't work even if the case diameter, .380" for the .38 round, were the same. I don't have any info on the case diameter of the Mak round. Of course, your premise is to use the moon clips for head spacing, but I still think the rim thickness of the .38 case would kill that idea.
I didn't think I'd ever see a revolver that looked so much like a broom handle mauser. :banghead:
