Only until 1883, I can not find any information prior, if FMJ ammuntion was being produced at all. Was Major Ruben of the Swiss laboratory at Thun, the first and only person to discover copper jacketed bullets?
copper jacketed bullets were not discovered, they were invented as a rational need, mainly by the french, when they discovered the leading caused by lead bullets at the speeds of smokeless powders in their Lebel rifles.
in the old west, when it comes to handguns, no copper bullets where used before 1890 as most revolvers were still black powder.
unfortunately, most italian clones of the 1873 peacemaker, have riflings more thought for modern jacketed or hard cast bullets and smokeless than for BP. .
original XIX century revolvers, until the 1920´s, have deeper riflings, that leaded less and stabilized better, and cleaned better.
and unfortunately most molds sold now, dont have deep enough grooves to avoid leading without adding tin to the mix, in most revolvers, when loaded with black powder. They are designed for smokeless powders. Lee´s molds, for instance.
all the best