A Sharps 1874 rifle is seen in the hands of some of Hearst's Pinkertons.
Winchester Model 1866 "Yellow Boy"
A few of Hearst's men carry Winchester Model 1866 "Yellow Boy" rifles.
Winchester Model 1873
Many characters carry the Winchester Model 1873 throughout the series, including several anonymous prospectors and townspeople. All of the Pinkertons called to Deadwood by Hearst in Amateur Night (3.09) carry Winchester '73s on their horses, prompting Tolliver to remark to Silas Adams that "All we need fear is their Winchesters." Johnny Burns and Dan Dority (W. Earl Brown) each take Winchesters when preparing for war against Hearst in The Catbird Seat (3.10).
Many characters carry and use Single Action Army revolvers throughout the show.
Cavalry Model
Calamity Jane (Robin Weigert) carries a Single Action Army Cavalry Model with a 7.5" barrel throughout the series. Wyatt Earp (Gale Harold) and Morgan Earp (Austin Nichols) each carry a Cavalry SAA when they arrive in Deadwood in "Leviathan Smiles" (S3E08). Hearst's man Barrett also has a Cavalry SAA, using it to shoot at Alma Garret Ellsworth in "A Constant Throb" (S3E10), and having it taken by Al Swearengen (Ian McShane), who taunts him with it before killing him.
When Sol is witnessed loading a Colt Thuer Derringer by Bullock in "Amateur Night" (S3E09), Bullock tells him to "stop thinking of that derringer as a problem solver". Trixie (Paula Malcomson) uses one during the third season, notably to wound George Hearst (Gerald McRaney) in "The Catbird Seat" (S3E11). E.B. Farnum (William Sanderson) draws his Colt Thuer when Odell confronts Hearst in "Unauthorized Cinnamon" (S3E05).
Colt 1860 Army (Richards-Mason cartridge conversion)
Dan Dority (W. Earl Brown) carries a Colt 1860 Army (Richards-Mason cartridge conversion) as his main sidearm throughout the show.
Colt 1849 Pocket
Al's man Davy draws a Colt 1849 Pocket in "I Am Not the Fine Man You Take Me For" (S3E02).
Remington 1866 Derringer
Joanie Stubbs (Kim Dickens) holds a Remington 1866 Derringer in "Tell Your God to Ready for Blood" (S3E01).
Remington 1875
Seth Bullock (Timothy Olyphant) carries a Remington 1875 throughout the series, including his term as sheriff of Deadwood. Dan Dority (W. Earl Brown) also occasionally carries a Remington 1875.
Smith & Wesson Schofield
Wyatt Earp takes one from the holster of the Pinkerton killed by Morgan in "Amateur Night" (S3E09) to make it look like Morgan fired in self defense.
Hearst's right-hand man Captain Turner (Allan Graf) holds a small pocket revolver on Swearengen during the election speeches in "I Am Not the Fine Man You Take Me For" (S3E02) before drawing his SAA Cavalry and pistol-whipping him with it.