As far as the cap and ball thing, it is very possible them using C&B revolvers in 1881, That is only 15 years beyond the civil war and there were plenty of them around. Some even favored them with an extra "conversion" cylinder for when cartridges were available. The .45 Colt was not even invented until 1872 and not in widespread use for a couple years after that.
Remember smokeless wasn't going to be around for a couple of years yet and not in widespread use until quite a while later. And we are talking about the "wild west" so most of these frontier towns were remote and didn't necessarily have a steady continuous supply of cartridges, but loose black powder and lead was always available in most towns of any decent size.
Remember Matty's "Colt's Dragoon" in True Grit? I'd say The Duke's cartridge guns may have been more out of place in that movie than her C&B, being it was set in 1870, a scant five years after the WBTS. Remember it wasn't until that year or actually December 11, 1869 that S&W's patent on bored through cylinders ran out. So, there would have been no Colt cartridge revolvers until the very year that movie was set in, and to have them in quantity that far away from the manufacturing facility that quick in the late 1800s, is dubious.
