Single Action Army revolvers are carried by several characters in the film, most notabley Ben Wade (Russell Crowe), whose gun has custom grips with gold crosses, nicknamed "The Hand of God". The gun is said to be cursed as anyone who touches it other than Wade dies. Wade keeps the gun in a special holster designed by Will Ghormley to have the old time look mixed with the advantages of modern quickdraw holsters (see here for more information). Crowe was trained in the film by Thell Reed, a world reknowned quick draw shooter labeled "Fastest Gun Alive" by the Colt company, who has worked as a weapons trainer in many films.
Smith & Wesson Schofield Model 3
Charlie Prince (Ben Foster) carries two Smith & Wesson Schofield Model 3 revolvers in butts-forward holsters also built by Will Ghormley (see more here). Thell Reed extensively trained Foster in multiple quick draw and spinning techniques to turn him into the cold-blooded killer Charlie Prince.
Spencer 1882 Shotgun
The Spencer 1882 Shotgun is an early pump-action shotgun carried by a deputy early in the film.
Colt Model 1855 Revolving Rifle
Mounted with a telescopic sight and carried by Ben Wade's Mexican sharpshooter.
I believe it was a cartridge version of some sort, towards the end it looks like he's punching out cartridges from his cylinder, after they shoot the rancher - ben
Why would they build a forend for the gun if you aren't supposed to put your hand in front of the cylinder. With handgun revolvers, doing this can lead to your hand being burned from the exhaust from the cylinder gap when the gun is fired, but if the gun sparked and fired all the chambers (chain fire), you're SOL no matter where your hand is. - Gunmaster45
Remington 1889 Double Barrelled Shotgun
A Remington 1889 double barreled shotgun sawed off to an extremely short length is carried by Byron McElroy (Peter Fonda) until his death and later by Dan Evans (Christian Bale).
If this is true, that's an anachronism. This movie takes place before '89. -GM
I believe you're mistaken. I have an 1878 Colt and believe that is what Fonda is using, which removes any concern about an anachronism. -RT
Yeeaaah, have you mistaken the 1878 Colt with the Remington 1889? Because I said the 1889 is an anachronism. I too believe this is a Colt 78 but why would I be mistaken? - Gunmaster45
Henry 1860
A Henry 1860 can be seen being cocked by a person when he hears the offer of 200 dollars to anyone who kills the person keeping Ben Wade (Russell Crowe) captive and is also used by other outlaws trying to kill Dan Evans (Christian Bale).