Howdy
This is a screen shot of Clint reloading his 1858 Remington with a fresh cylinder loaded with cartridges in Pale Rider.
The prop guys converted a Cap & Ball 1858 to accept cylinders for cartridges. It may have only been capable of shooting blanks, I don't really know.
Smith and Wesson was the licensee to the Rollin White patent for revolvers with bored through chambers that could accept cartridges. This patent expired in 1869. As the patent licensee, in February of 1868 S&W signed a contract with Remington allowing Remington to alter a total of 4,574 Cap & Ball revolvers to fire cartridges. Remington did the conversions at their factory in Ilion NY. New five shot 46 rimfire cylinders were used. S&W received a $1.00 royalty on each revolver converted. These are the revolvers that were the historical basis for what Clint was shooting in Pale Rider.
In addition, after the White patent expired in 1869, many gunsmiths did their own conversions of the 1858 Remington to cartridges.
Aguila Blanca is correct about the bore diameter of 44 caliber Cap & Ball revolvers and the development of the 44 Colt cartridge.
This is a Colt Richards Conversion. Not the Richards-Mason Conversion, that came a few years later. This is basically a 1860 Army Cap & Ball Colt that has a been converted to shoot cartridges by substituting a cartridge cylinder, adding a conversion ring behind the cylinder, and removing the loading lever and adding an ejection rod. Four original 44 Colt cartridges are pictured with it.
Colt produced three or four different 'cartridge conversion' revolvers before finally bringing out the Single Action Army in 1873, four years after the White patent had expired. It is true that after the end of the Civil War Cap & Ball revolvers were a glut on the market, and it was often cheaper to buy one of them and convert it to firing cartridges than it was to buy a new cartridge revolver.
Because the groove diameter of 45 Colt is .451, and the groove diameter of '44' caliber Cap & Ball revolvers is the same, or very nearly the same, several manufacturers started businesses about 20 years ago or so producing cartridge conversion cylinders for modern reproductions of Cap & Ball revolvers. Ken Howell was one of these guys, Walt Kirst was another.
This is an Italian replica of the 1858 Remington Cap & Ball revolver with a 45 Colt conversion cylinder made by Ken Howell.
This is how you load it. You drop the loading lever to free the cylinder pin, pull out the cylinder pin and pull out the cylinder. The cap with six independent firing pins is a slip fit and you pop it off, load five (not six) cartridges and pop everything back in place. Of course you are careful to position the empty chamber under the hammer.
These conversion cylinders are made of modern arsenal steel and are safe to shoot with mild Smokeless ammunition, but I only shoot mine with ammo loaded with Black Powder.
The Kirst system is a bit different. He uses a conversion ring mounted to the frame with a single firing pin, very similar to the Colt Richards Conversion. The cylinder can be reloaded on the gun by carving a loading groove onto the frame, enlarging the groove already there for loading caps onto the nipples.
It is true that one can buy a Cap & Ball revolver and legally convert it to a cartridge firearm by adding a conversion cylinder, at least in the eyes of the BATF. State laws may vary. Technically, when you put in the conversion cylinder you have transformed it to a cartridge firearm, if you put the original Cap & Ball cylinder back in you have made it a non-firearm again. There are some legal difficulties though if you alter the frame in anyway, such as carving a loading slot.