"Jack Slade mistakes
Factual error: After they bury Jack's father, the stage driver hands Jack what he refers to as a "Navy" Colt. However, in 1841, the only colt handguns were a handful of Paterson revolvers, usually carried by Texas Rangers, and in fact, the revolver handed to the boy was a cartridge weapon.
Factual error: As a boy in 1841, Jack and his father take passage on an Overland Stage Company coach. However, this company wasn't in existence until the late 1850's."
XD-40 service, XD-9sc, member GeorgiaCarry.Org, National Rifle Association, Gun Owners of America, North American Hunting Club, Rocky Mountain Elk Foundation
From the poor movie poster it could be a colt navy or colt paterson. Most likely from one of the actual photos none of which are good enough to really see it was a modern revolver with parts welded on to look like a colt navy.
According to the story the father gave the son(slade) a colt navy .36 caliber revolver. What the movie people actually used was a prop made to loosly resemble one.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...
From the rather poor poster illustrations, my guess would be that the gun is a Colt Single Action Army, modified to look like a Remington cap-and-ball revolver.
Years ago antique dealer Robert Abels had some studio prop guns that had been modified. The most numerous were Colt New Service or S&W Hand Ejector models fitted with fancy grips and fake ejector rod housings.