Gun
The gun is an item that can be found in Diamondback.
Background
It is a six-shooter revolver that belonged to the previous Diamondback sheriff, Bill Purvis. It is available during the daylight hours of Day 2, and can be found in the bucket of the well near Pig Farmer Quist, who has kept it in secret since the late sheriff's death. As he is very protective of the hidden weapon, The Stranger must wait until Quist is distracted by a conversation with Ned DeVries before it can be retrieved.
The gun is a key item in the game, and must be retrieved to advance the story. Finding a weapon is one of four tasks given to The Stranger by Jackalope Jones the morning after the former's arrival in Diamondback. There are several opportunities to use the gun, such as defending Help's Curiosity Shop against Cobb and Dale Belcher, and two shootouts; one against corrupt bounty hunters searching for Hirotedus Mezamee, and against The Kid and his gang of outlaws. The shooting range can be used to practice for these events.
Once the gun is equipped, it can be clicked on in the player's interface to switch between unholstered and holstered. The player can then shoot almost anywhere on the screen until the gun is out of bullets. To reload, the gun in The Stranger's hand can be clicked to swing out the cylinder where the chambers can be clicked up to six times. The gun must be reholstered before people and objects can be interacted with normally.
Shooting at innocent people or animals will cause the game to end, as it will lead to deadly retaliation from the citizens of Diamondback.
Ruby's Gun
A second gun can be found in Ruby's room at the Hard Drive Saloon. After smooth talking her, The Stranger can give her Flowers found in Shady Acres Cemetery, causing her to leave momentarily in search of some water to keep them in. Once she leaves, her room may be entered and the gun can be found in her drawer next to a bible. The Stranger does not need to take the gun, but once he leaves the room, Ruby will return and he will not be able to explore the room again. Whether he takes the gun or not, Nate Trotter will be downstairs, and upon seeing The Stranger, will shoot him in a jealous rage for spending too much time with Ruby.
Notes
Guns are banned in Diamondback by order of Mayor Macintosh, but, according to him, it seems "not everyone's heard that," judging by numerous gunshots heard throughout the game, and the fact that numerous citizens are seen with a weapon.