Bret Maverick (Mel Gibson) carries a Single Action Army "Artillery" model with a five inch barrel as his sidearm. Maverick evidently keeps it with all six loaded, as opposed to many actual Old West gunfighters, evident in the scene in which Annabelle Bransford (Jodie Foster) accidentally discharges his revolver when she falls on his holster and when Maverick tells her and Coop that he has "six bullets" when facing off against the bandits (although he fires many more than six shots without reloading). actually he fired it six times and picked up another gun.
Single Action Army "Quickdraw"
Several characters, most notably the bank robbers who hold up Maverick, carry the "Quickdraw" model of the Single Action Army revolver.
Henry 1860
Angel (Alfred Molina) loads a Henry 1860 onto his horse before he fights Maverick's cronies.
Remington 1875
Marshal Zane "Coop" Cooper (James Garner, who played Bret Maverick in the original TV series) carries a nickel Remington 1875 as his primary sidearm.
Colt Single Action Army Bisley
Marshal Zane Cooper (James Garner) keeps a Bisley Colt SAA with white grips as his backup weapon, which Maverick (Mel Gibson) grabs and fires during the confrontation aboard the Lauren Belle after the poker game.
It looks more like it just had Bird's Head grips, the frame doesn't have any hump like a Bisley does. - Gunmaster45
could it be a colt lightning?
I'd definitely say colt lightning, or maybe modern replica, can't tell if it has the DA or SA trigger, definitely NOT a bisley -Pawnstar
Pawnstar is right it's not a Bisley gripped Colt, but it's also not a true Bird's Head either. In fact it strongly resembles the grip frame on made for Doc Holiday's (played by Val Kilmer)Stainless steel Ruger Vaquero in the film Tombstone, Holiday is to carry a Double action Colt Lightning, with Birds head grips. The holster that Coop is wearing is also what is commonly known as a "Doc Holiday" shoulder rig.
Sharps Pepperpox Pistol
Mrs. Annabelle Bransford (Jodie Foster) keeps a Sharps Pepperbox, which she lends to Maverick (Mel Gibson) to use during his battle with the outlaws. A woman ejected from the poker game on the Lauren Belle also has a Sharps in her purse, which falls out.
Winchester Model 1873
One of the outlaws Maverick fights and one of the women robbed by the outlaws each have a Winchester Model 1873.
The Russian Grand Duke (Paul L. Smith) has a Kentucky Flintlock Rifle when Joseph tells him to go hunting for an "Injun'" (Maverick in disguise) in order to get back the money to pay Maverick.
Commodore Duvall (James Coburn) uses a Sharps 1874 with a telescopic sight when chasing after Coop.
Colt 1851 Navy (Richards-Mason Conversion)
Commodore Duvall (James Coburn) confronts Marshal Cooper with a Colt 1851 Navy with a Richards-Mason cartridge conversion. Maverick takes the revolver when he comes across them.