And somehow Europeans suddenly switched over in one felled swoop? BS. I'm sure it was a gradual transition as well and perhaps even slower as they weren't conquering any frontiers full of hostile indigenous peoples within the boundaries of Europe then.
the period between 1820-1871 was one of the most turbulent times in European History, with countries fighting againts each other, in some times small , and sometimes brutal and total destruction wars that configurated the borders of Italy, Germany, France, Denmark, Austria .....such as we know them today (well, almost) plus the colony and imperial wars overseas..
That led to an arms race among the main european powers, specially France and Prussia with many radical designs and experimentation, too many to mention here .
in short, changes were fast and what was ok in 1865, by 1868 could be old fashioned.
Cap and ball revolves were obsolete in Europe for military and civilian use in 1860 . The french tested the Lefaucheux in Crimea and adopted if for the Navy in 1856. The spanish did it 2 years later..labelling their army issue Adams type revolver, as "obsolete" in 1858.
The great amount of surviving examples of Lefaucheux and rimfire, and later centerfire revolves, in the period of 1860-1870 proofs that they were very popular in Continental Europe, but not so in the Uk and the USA, were more powerful arms were very appreciated.
so I think that the change was fast. As soon as there was a working design avaiable by a major manufacturer and money to buy it, everybody threw their cap and ball away and bought the metallic cartridge.
that was specially truth among army officers, who were involved, as I said, in continous fighting, be it againts native or european enemies, and who allways wanted the latest technology avaible. And lets remember that they had freedom, in many cases, to buy their personal revolver, as long as it met the caliber criteria.
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anyway, I cant imagine an outlaw in 1871 in Kansas state, with a Tranter 1868 revolver. it would make a lot more sense that he was using a cap and ball, ready avaiable and probably cheap with caps and powder allways avaiable.
however, I can imagine a wealthy US army high rank officer in 1870 with a Webley Bulldog revolver. Why not?
if you had the money, I am sure that you could buy the latest centerfire revolver in 1869, for example, coming from the UK in any good gun shop in either San Francisco or Salt Lake city.