A rule of thumb, is rimmed rounds go in revolvers, and rimless rounds to in semi-auto's. But like all rules of "thumb".. there are exceptions. But when you get down to these kind of details you should be educated enough to know about these few exemptions. For instance there are one or two 9mm parabellum revolvers that are made to take the rimless 9mm semi-auto rounds. There were revolvers that could take .45acp rimless rounds with the aid of half moon or full moon clips. and I can think of at least one old obscure semi-auto that uses 38 special rimmed cartridges, and of course the Automags of various permutations that use the rimmed .44Magnum normally a revolver cartridge. Of course there is the ubiquitous .22LR which is rimmed, which fit rifles, pistols and revolvers. Of course there custom guns that can be made to chamber whatever you want.. but still the rule of thumb will serve the average person well.
