Well, basically, a minister invented the percussion cap back in the early part of the 19th century, as a self contained replacement for flint. So to fire your BP firearm, you would have a percussion cap placed on a nipple (which has a small hole in it to transfer the flame down to the BP in the chamber of the firearm. Think of it as an early primer and you have the right idea. Lot's of Italian made copies of C&B revolvers around, Uberti makes a nice one, but there are lots of other makers. Conversions came along in the late 1860's, to take advantage of self contained cartridge technology with C&B revolvers. Richards conversions were popular (he was one of the guys who ran Colt after Samuel died. Sam Colt passed on the self contained cartridge idea, one of his employee's brought it to him, Rollin White if memory serves, and he turned down the idea, so White took it to S&W. Bad move on Colt's part, but in his defence, he was in the middle of supplying the US gov't for the war of northern aggression at the time and probably couldn't drum up the production capability. FWIW - dan