In the pilot episode, Byron Sampson (Christopher Darga) leads his lynch mob to Bullock's jail with a Henry 1860 (specifically, his is an steel frame, rather than the usual brass). Several townspeople in Deadwood can also be seen with Henry rifles, most notably a man walking behind Ellsworth and Alma in A Lie Agreed Upon, Pt. 1 (2.01).
Snider-Enfield Mk.III Cavalry Carbine
A man in Nuttall's saloon places a Snider-Enfield carbine on a table when Nuttall is showing off his new bicycle in Childish Things (2.08).
Winchester Model 1866 "Yellow Boy"
One of Tolliver's men at the Bella Union fires a Winchester Model 1866 "Yellow Boy" into the air to celebrate and announce its official opening at 8:00 p.m. in Reconnoitering the Rim (1.03). In The Trial of Jack McCall (1.05), Tom Nuttall (Leon Rippy) places a Model '66 inside "Wild Bill" Hickok's casket. Trixie (Paula Malcomson) aims a Winchester '66 during Bullock's confrontation with Swearengen in A Lie Agreed Upon, Pt. 2 (2.02), telling Sol the recoil would be too much for him to handle if he had to fire it. A few of Hearst's men in the third season also carry Winchester 1866 rifles.
Shotguns
Rossi Overland double-barreled shotgun
Both Seth Bullock (Timothy Olyphant) and Sol Star (John Hawkes) wield Rossi Overland Coach Guns with exposed hammers in the pilot episode to keep the lynch mob away. Dr. Amos Cochran (Brad Dourif) also grabs one when defending Sofia Metz (Bree Seanna Wall) from Swearengen's men in Deep Water (1.02). Dan Dority (W. Earl Brown), Al Swearengen (Ian McShane), Charlie Utter (Dayton Callie), and Calamity Jane (Robin Weigert) all carry or use shotguns in A Lie Agreed Upon, parts one and two. Hostetler (Richard Gant) and self-proclaimed "General" Samuel Fields (Franklyn Ajaye) fight over one in Advances, None Miraculous (2.10). Louis the Bank Guard (Franc Ross) carries one when greeted by Alma in Amateur Night (3.09).
Handguns
Colt Sheriff's Model Single Action Army
A gun salesman seen while Seth Bullock rides into town in the pilot episode is showing off a Colt Sheriff's Model Single Action Army with a 3.5" barrel. Trixie (Paula Malcomson) gives a wounded Sol Star (John Hawkes) one to help defend Bullock in A Lie Agreed Upon, Pt. 2.
Richards-Mason Conversion Colt 1860 Army
Dan Dority (W. Earl Brown) has a Colt 1860 Army (Richards-Mason cartridge conversion) as his main sidearm throughout the show. During the pilot episode, Ned Mason (Jamie McShane) carries a Colt Army. Whitney Ellsworth (Jim Beaver) also uses one when chasing Francis Wolcott away from the Garret mine in Requiem for a Gleet (2.04).
Colt 1849 Pocket
Al's man Davy draws a Colt 1849 Pocket in I Am Not the Fine Man You Take Me For (3.02).
Pinfire pocket revolver
The so-called "derringer" that Trixie (Paula Malcomson) uses to shoot and kill one of her customers at the Gem Saloon in the pilot episode actually appears to be a Pinfire revolver, which Al Swearengen (Ian McShane) takes from her. This was based on a real-life incident in Deadwood in which a prostitute shot one of her clients through the head and he survived for twenty minutes, muttering.
Colt 1851 Navy
James Butler "Wild Bill" Hickok (Keith Carradine) carries a matched pair of ivory-handled Colt 1851 Navy revolvers until his death in Here Was A Man (1.04). During Reconnoitering the Rim (1.03), Hickok is playing a game of poker with Jack McCall (Garret Dillahunt) in Nuttall's No. 10 saloon when he is down to his last eight dollars, putting one of his Colt Navy's on the table to bet it. McCall tells Hickok that his Colt is worth at least $40 more than his raise, putting up $50 more if Hickok will place both guns on the table. This prompts Hickok to quickly draw his other Colt Navy, scaring the other players, until he puts it on the table with his other, winning the bet with a flush of clubs.
Remington 1866 Derringer
Trixie (Paula Malcomson) receives another gun, a Remington 1866 Derringer, from Jewel "the gimp" (Geri Jewell) but gives it to Swearengen at the end of the pilot episode. (However, a continuity error switches this gun to both an NAA Mini-Revolver and a Smith & Wesson Model 1 at the beginning of the next episode). Cy Tolliver (Powers Boothe) uses a derringer to kill Miles Anderson (Greg Cipes) in Suffer the Little Children (1.08), but this too becomes a S&W Model 1 when he hands it to Joanie Stubbs (Kim Dickens), who later conceals a black-gripped derringer in New Money (2.03). In Something Very Expensive (2.06), Maddie (Alice Krige) unsuccessfully threatens Francis Wolcott (Garret Dillahunt) before he takes it from her.
Colt 1851 Navy Richards-Mason Conversion
When Calamity Jane (Robin Weigert) draws and re-holsters her revolver on Doc Cochran in the pilot episode, it is a Colt 1851 Navy with a Richards-Mason cartridge conversion. When the scene is shown from her POV, she has her regular SAA Cavalry Model. The shots of Jane with the Colt Navy are a continuity error.
Single Action Army
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. Captain Joe Turner (Allan Graf), one of Hearst's men working for Wolcott, uses a Cavalry Model to shoot and kill a naked Cornishman who tried to steal gold in Childish Things (2.08). Wu's rival, Mr. Lee (Philip Moon) uses a Cavalry Model to kill one of Wu's men in Boy-the-Earth-Talks-To (2.12). Wyatt Earp (Gale Harold) and Morgan Earp (Austin Nichols) each carry a Cavalry SAA when they arrive in Deadwood in Leviathan Smiles (3.08). Hearst's man Barrett also has a Cavalry SAA, using it to shoot at Alma Garret Ellsworth in A Constant Throb (3.10), and having it taken by Al Swearengen (Ian McShane), who taunts him with it before killing him.
Artillery Model
Charlie Utter (Dayton Callie) carries a Single Action Army Artillery Model with a 5.5" barrel throughout the series. Jack McCall (Garret Dillahunt) murders "Wild Bill" Hickok with an Artillery Model in Here Was a Man (1.04). According to contemporary reports, the real Jack McCall had used a double-action .45 caliber revolver to murder Hickok. In Sold Under Sin (1.12), several Cavalry soldiers and a man assisting Con Stapleton use Artillery Model SAAs. Dan Dority (W. Earl Brown) offers one to Swearengen in A Lie Agreed Upon, Pt. 2 (2.02) to face Bullock but Swearengen declines. Eamon (Jeff Cahill) attempts to draw one as Dan cuts his throat in Requiem for a Gleet (2.04), but it drops to the ground. Mose Manuel (Pruitt Taylor Vince) has an Artillery Model which he uses to shoot his brother during Nuttall's bicycle demonstration in Childish Things (2.08), later worrying to Wolcott that someone will discover the bullet in his brother's body as his own. Tom Nuttall (Leon Rippy) secures his SAA behind his bar in Full Faith and Credit (3.04).
I'm pretty sure all of these are 5" models, which implies they are newer reproductions. All along I thought the artillery was 5", but I discovered it is 5.5". I have lots a edits to change. - Gunmaster45
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
Al Swearengen (Ian McShane) keeps a Smith & Wesson Schofield on his nightstand in the pilot episode, which he pulls under the sheets when Trixie enters his room. Wyatt Earp takes one from the holster of the Pinkerton killed by Morgan in Amateur Night (3.09) to make it look like Morgan fired in self defense.
Colt New Line
After Trixie places her derringer on Swearengen's nightstand in the pilot episode, he wakes up the next morning (in the episode Deep Water (1.02)) and picks it up, asking if it was "for him". However, a continuity error occurred and the pistol became an .22 caliber Colt New Line before turning into a S&W Model 1 in the next shot.
Smith & Wesson Model 1
In a three-part continuity error, Trixie's Remington Derringer/Colt New Line is now a Smith & Wesson Model 1 in a shot in Deep Water (1.02). Cy Tolliver (Powers Boothe) hands Joanie Stubbs (Kim Dickens) a Model 1 to murder Flora Anderson (Kristen Bell) for attempting to steal from the Bella Union in Suffer the Little Children (1.08). The pistol originally used by Cy to kill Flora's brother Miles was a Remington Derringer, but it is possible (although not likely) that he pocketed the derringer and gave Joanie a S&W Model 1 to shoot Flora.
Colt Walker
The preceding judge at McCall's trial (for Hickok's murder), Magistrate Claggett (Marshall Bell), in The Trial of Jack McCall (1.05) uses a Colt Walker as a makeshift gavel.
Winchester Model 1873
Many characters carry the Winchester Model 1873 throughout the series, including several anonymous prospectors and townspeople. Charlie Utter (Dayton Callie) pulls a Model '73 from his saddle bag when he sees Bullock beaten by the Indian in Plague (1.06). Whitney Ellsworth (Jim Beaver) carries a Winchester '73 in A Lie Agreed Upon, Pt. 1 (2.01). Johnny Burns (Sean Bridgers) uses one in the same episode during Bullock's fight with Swearengen, wounding both Sol Star and Charlie Utter with it. Calamity Jane (Robin Weigert) holds a Winchester on Francis Wolcott in Childish Things (2.08) as Wolcott is leaving the Chez Ami. 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).
Sharps 1874
A Sharps 1874 rifle is seen being sold on a rack above a Sharps carbine in Suffer the Little Children (1.08). In Jewel's Boot is Made For Walking (1.11), a Sharps is seen hanging on the wall in Cy Tolliver's office in the Bella Union. Some of Hearst's Pinkertons in the third seasons also carry Sharps rifles.
Sharps 1874 Cavalry Carbine
A Sharps 1874 Cavalry Carbine rifle is seen being sold on a rack below a Sharps 1874 in Suffer the Little Children (1.08).
Sol Star (John Hawkes) carries a Colt Thuer Derringer in A Lie Agreed Upon, Pt. 1 (2.01), but it proves useless. When Sol is later witnessed loading it by Bullock in Amateur Night (3.09), 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 (3.11). E.B. Farnum (William Sanderson) draws his Colt Thuer when it Odell confronts Hearst in Unauthorized Cinnamon (3.05).
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 (3.02) before drawing his SAA Cavalry and pistol-whipping him with it.