Matthew Quigley (Tom Selleck) uses a Shiloh Sharps 1874 Long Range rifle with a 34" barrel (4"s longer than a standard 30" barrel) converted to fire a .45-110 metallic cartridge with a 540 grain paper-patch bullet. It has double set triggers, and is fitted with a ladder-elevated Vernier peep sight and a Globe front sight. He is an incredible sharpshooter with this rifle and often makes use of the double set triggers for more accurate shots. Sometimes he shoots from so far away, the report of the rifle is heard 2-3 seconds after the impact of the bullet (Even though sound catches up with supersonic rounds after 300-400 yards). Several times in the film the gun is shown capable of sending people airborne (some even completely flipped in mid-air!), as movie rules states a big gun must send bad guys flying.
At one point in the film, we have some excellent gun dialogue seldom seen in most movies, in which Quigley explains his rifle to Marston.
Breech Loader
Cartridge
Barrel
Double Set Triggers
Sight
Colt 1860 Army
Elliot Marston (Alan Rickman) uses a Colt 1860 Army .44 caliber as his personal sidearm. He refers to it as the Army revolver and has much respect for its maker, Colonel Samuel Colt. He gives his second one to Quigley in the final duel, thinking he is bad with revolvers based on how he said he never had much use for one. When Quigley defeats him and his two men he says, "I said I never had much use for one. Never said I didn't know how to use it." He pockets the revolver, then realizing he found a reason to use one.
Griswold & Gunnison 1860
Marston's men are mainly armed with reproduction Griswold & Gunnison 1860 revolvers in .36 caliber throughout the film. They are not Colt 1851s as previously noted due to their round barrels and brass frames.
Colt 1851 "U.S. Marshal"
Dobkin (Tony Bonner) carries a pocket version of the 1851, known as the Colt 1851 Navy "U.S. Marshal" with ivory grips and cylinder grooves which Quigley also pockets for himself after the final duel.
Colt 1862 Pocket Navy
One of Marston's men tries to draw a "belly gun", a Colt 1862 Navy, from the small of his back before being shot by Quigley.
Marston's men arm themselves mainly with Thompson Center Arms Hawkins Plains rifles throughout the film. Quigley kills one of these men and takes the rifle off his horse for Crazy Cora to use.
Bounty Hunter Dueling Pistol
The gunsmith of the town offers Quigley a Italian .45 caliber dueling pistol, called simply the "Bounty Hunter", but he refuses, claiming he never had much use for a shooter(pistol).
Colt Dragoon 1848
Quigley also takes off the dead man's horse a Colt Dragoon 1848 .44 caliber pistol. Crazy Cora (Laura San Giacomo) uses the Colt Dragoon to fend off dingos from her camp and an Aborigine baby while Quigley is away getting .45-110 shells from a town. Presumably the same man who owned the horse is seen cocking the gun on the wagon as the Red-coats aproach.
Colt Walker 1847
A full-sized original Colt Walker 1847 is seen in the hands of one of Marston's men during the shootout in in the town with Quigley. The Colt Walker used is most likely a reproduction. Only about 1100 where originally made and they now sell for US$150,000 or more.
At the end of the film when Quigley is preparing to leave Australia, the travel clerk cocks a Hoppes Model 300 Ethan Allan boot pistol (source, 3rd Ed. Black Powder Gun Digest, page 16) under his counter when asking his name, aware there is a bounty on Quigley.