Wyatt Earp (Kevin Costner) is seen multiple times through out the film using Single Action Army revolvers. Mid-way through the film he is seen to have selected to keep a Buntline special with an 8" barrel as his right hand gun and an Artillery with a 5" barrel as his left hand gun. Apprently at some points in the film the actual Buntline used by Earp was taken out of the Wyatt Earp Museum and used by Costner for some closeup shots. Multiple other characters are also seen using SAAs throughout the film.
Colt Sherrif's Model Single Action Army (3.5" barrel)
John "Doc" Holiday (Dennis Quaid) uses a Colt Sheriff's Model SAA revolver with a 3.5" barrel and nickel finish as his weapon of choice and uses it several times in the film, including the infamous Gunfight at the O.K. Coral. Historians have proven that during the gunfight, Doc Holiday was actually using 7.5" Cavalary SAA, not a Colt Sheriff's Model. He was believed to have carried a Cavalary SAA right up until he died in the sanitarium at age 36.
Starr 1858 Army
At a young age Wyatt Earp (Kevin Costner) is seen with a Starr 1858 Army double/single action percussion revolver tucked in his belt.
Stevens 10ga Double Barreled Shotgun
The gun given to Doc Holiday by Virgil Earp is a Stevens 10 gauge shotgun right before the Gunfight at the O.K Coral and Doc uses it to shoot and kill Curly Bill Brocius. According to historians the gun was borrowed by Wyatt Earp from Fred Dodge and was infact used during the infamous gunfight.
Colt Model 1878
A Colt Model 1878 Shotgun is seen used by Wyatt Earp several times in the film including stopping Ruffians in Dodge City and killing assassins during the Canyon Ambush.
One of the assassins who shoots Virgil Earp and cripples his right arm is using a Sawed-Off Shotgun.
Remington 1875
Wyatt Earp (Kevin Costner) uses a Remington 1875 revolver early in the film and draws it to hold up a man who tries to force him to drink whiskey and goes for his gun when he denies.
Colt 1851 Navy (w/ Richards-Mason conversion)
A man named Ed Ross (Martin Kove) tried to draw his Colt 1851 Navy revolver with a Richards-Mason Cartridge Conversion. Instead of drawing his Starr revolver, Wyatt grabs a Pool ball and throws it at the man's thoat instead. He then takes the gun for himself and practices drawing it during the Fourth of July fireworks show. Based on Wyatt's age and the time, this gun is likely an anachronism.
Colt 1860 Army (w/ Richards-Mason conversion)
Two drunkards settle an argument at the start of the film by drawing Colt 1860 Army revolvers with Richards-Mason cartridge conversions (which are anachronistic to the time). The unruly man who tries to force Wyatt to drink whiskey tries to reach for a nickel Army cartridge gun but Wyatt draws faster and makes him leave. Big Nose Kate (Isabella Rossellini) is later seen using one, which she fired some shots at Doc Holiday for slapping her, but Earp knocks Doc out and take the gun from her.