It all depends on what time period that YOU are portraying. Firearms of all types were used for a long time, even after newer or more modern models came into existence. So for whatever time period you place yourself in, you can shoot anything made up to that point, but nothing that came later. In 1866 your handguns would all be percussion. Conversions and cartridge opentops came around '71, and then in 1873 the SAA came along, although pretty expensive and not really available to the public at first. I've been talking about Colts, but other makers will be similar time period. So in 1871 or later you might have a '66 and an Opentop, as they could shoot the same ammo. Of course your modern versions can be .38's, but the guns are still the same models as back then. And in 1880 you might have a '73 and SAA both in 44-40...or you might still be shooting that trusty ol' '66. Percussion and conversion pistols were a lot more common in the old west than SAA's, despite Hollywood.