I've read that the reason they used Trapdoor Springfields in some scenes in The Outlaw Josey Wales was because its safer to fire a blank cartridge than to fire a blank-loaded muzzle loader. I guess maybe the blank cartridge doesn't need a wad or as much of one because it can be crimped? Anyway, if you look closely you'll see that they are shooting Trapdoor Springfields from inside the house.
The still pictures and closeups show a regular Colt Walker and the other, lesser, revolvers but the shooting scenes were done with revolvers converted to fire cartridges for the same reason.
That same issue may have had something to do with the prevalence of guns from the future in so many other movies as well.
The older movies just didn't have the attention to detail on firearms that the newer ones do. Josey Wales was made during a time when movies were transitioning to much more accurate depictions, so the movie is interspersed with guns that were easy to work with and guns that are historically accurate. The Navajo woman's pistol, when she gets the drop on Lone Waite, is obviously a conversion.
One thing about Josey Wales, it is unclear what year it is. Allin Conversions came out in what? 1866? It could easily have been 1866 and the guns came from the Commanchero's stock-stuff that could have been stolen or bought from rogue elements of the US Army. The cartridge conversion pistols are a big stretch though. So is the model 1874 Sharps, which actually came out in 1871.
