Deputy US Marshal Raylan Givens (Timothy Olyphant) and nearly all of the other US Marshals in the series carry the full size Glock 17 as their sidearms, including Chief Deputy Art Mullen (Nick Searcy) and Deputy Marshal Tim Gutterson (Jacob Pitts). In "Truth and Consequences" (S4E03), FBI Special Agent Alex Barnes (Josh Stamberg) is seen pulling out his Glock 17 when he's confronted by Raylan.
Glock 26
The Glock 26 appears in the series mainly as the sidearm carried by Deputy Marshal Rachel Brooks (Erica Tazel). The Glock 26 also is the pistol Raylan keeps as his backup as well. In "Hole in the Wall" (S4E01), Raylan pulls his Glock 26 when confronting Jody Adair (this pistol appears to be an airsoft replica). The same pistol appears to be pulled by Tim Gutterson in "Foot Chase" (S4E06).
Beretta 92FS
The Beretta 92FS is used by several characters in Season 4, notably Boyd Crowder (Walton Goggins). In "Hole in the Wall" (S4E01), a Beretta 92FS is used by Benny (Casey Brown) while in a confrontation with Raylan. Boyd is seen pulling it in "Where's Waldo?" (S4E02).
Beretta 92FS Inox
The Beretta 92FS Inox also is used by several characters in Season 4. A Beretta 92FS Inox is pulled by Jody Adair (Chris Chalk) in "Hole in the Wall" (S4E01). Jimmy (Jesse Luken) is seen pulling an Inox in "Where's Waldo?" (S4E02). One of Nicky Augustine's thugs threatens Raylan and Winona with the Inox in Season 4's finale "Ghosts" (S4E13). Raylan later uses the pistol and correctly identifies it as a Beretta to Nicky later in the episode.
Beretta 8045 Cougar
Sheriff Shelby Parlow (Jim Beaver) appears to carry a Beretta Cougar as his sidearm in Season 4. He fires the pistol in "Foot Chase" (S4E06).
EKOL Grizzly Special 99
In "Hole in the Wall" (S4E01), what appears to be a small compact pistol is pulled by the scrapyard operator while threatening Constable Bob Sweeney (Patton Oswalt). Upon closer inspection, the pistol appears to be an EKOL Grizzly Special 99, a blank-firing handgun. This pistol apparently was in Sweeney's "go-bag". Sweeney uses the pistol while in a shootout in "The Hatchet Tour" (S4E09). In "Foot Chase" (S4E06), what appears to be a nickel Beretta 85F is pulled by a drug dealer. In reality, this is a nickel model of the EKOL. This pistol is later seen in the hands of Colton Rhodes (Ron Eldard) in "Outlaw" (S4E08).
M1911A1
In "Hole in the Wall" (S4E01), Boyd Crowder is seen giving an M1911A1 to Colton Rhodes (Ron Eldard).
Heckler & Koch USP
In "Money Trap" (S4E07), a Heckler & Koch USP is seen in the hands of Jody Adair (Chris Chalk) after taking it off a bail bondsman.
SIG-Sauer P226R
In "Kin" (S4E05), Nicky Augustine (Mike O'Malley) appears to pull a SIG-Sauer P226R. In "Decoy" (S4E11), a thug named "YOLO" also has a SIG that is later used by Bob (Patton Oswalt).
SIG-Sauer P230
In "Money Trap" (S4E07), Sharon Edmunds (Aja Evans) is seen pulling what appears to be a SIG-Sauer P230 during a confrontation with Jody Adair.
TSD Caspian WE Hi-Capa Airsoft
In "Outlaw" (S4E08), a Detroit hitman disguised as a Harlan County deputy uses a small compact pistol that resembles a Colt Commander as his weapon of choice. Upon closer inspection, the pistol appears to be a TSD Caspian gas blowback airsoft pistol. The same pistol is seen in the Season 4 finale "Ghosts" (S4E13).
Walther PPK replica Kimar "Lady K"
In "Where's Waldo?" (S4E02), Wynn Duffy (Jere Burns) is seen using what appears to be a Walther PPK during a confrontation with Boyd. Due to the close proximity to another actor, this pistol is most likely a Kimar "Lady K" an 8mm blank fire only Walther PPK replica.
A Smith & Wesson Model 36 is seen in the hands of Ellen May (Abby Miller) when one of her customers surprises her in a bear suit in "Hole in the Wall" (S4E01).
Smith & Wesson Model 30
A member of the Truth family is seen holding a Smith & Wesson Model 30 when confronted by the Marshals in "Where's Waldo?" (S4E02). Art is seen later unloading the revolver.
Smith & Wesson Model 317
Milo Truth is seen pulling what appears to be a Smith & Wesson Model 317 in "Where's Waldo?" (S4E02). This also appears to be the revolver held by Ava Crowder (Joelle Carter) in "Peace of Mind" (S4E12).
Shotguns
Mossberg 500AT
The Mossberg 500AT shotgun is seen in "Where's Waldo?" (S4E02).
Mossberg 590 Mariner
In "This Bird Has Flown" (S4E04), Rachel gives a pistol-gripped Mossberg 590 Mariner to Raylan, who is seen using it in a confrontation with Randall Kusik (Robert Baker). Lindsey Salazar (Jenn Lyon) is also seen using the shotgun.
Remington 870 Police
A Remington 870 Police model with a dedicated forend weaponlight is carried by Tim Gutterson in "Where's Waldo?" (S4E02).
Remington 870 (Short Barrel)
In "The Hole in the Wall" (S4E01), Ava Crowder is seen pulling a short barrel Remington 870 from underneath the bar counter. This short barrel Remington also appears to be carried by Jimmy (Jesse Luken) as he searches a revival tent in "Truth and Consequences" (S3E03).
Over/Under Shotgun
12 Gauge Over/Under Shotguns are seen in the hands of several characters in Season 4. In "Outlaw" (S4E08), Frank Browning (Rocky McMurray) is seen cleaning and holding his shotgun while in a conversation with Boyd. In "The Hatchet Tour" (S4E09), Lee Paxton (Sam Anderson) holds one while speaking with Constable Bob Sweeney (Patton Oswalt).
Rifles
Colt M4A1
In "Peace of Mind" (S4E12), Nicky Cush is armed with an M4A1 when he confronts Boyd and Picker (John Kapelos).
Ruger Mini-14
A scoped Ruger Mini-14 is seen used by one of Nicky Augustine's men in "Decoy" (S4E11). Colton is also seen using the rifle later in the episode. Jimmy (Jesse Luken) holds the rifle in Season 4's finale "Ghosts" (S4E13).
Remington 700PSS
In "Decoy" (S3E11), Deputy Gutterson uses the Remington 700PSS to put holes in the gas tank of an abandoned car.
Steyr Scout
In "Outlaw" (S4E08), Frank Browning's bodyguard Deke is seen holding a Steyr Scout.
Other
Frank Browning Rifles
In addition to his shotgun, Frank Browning also places several rifles and shotguns on a table in "Outlaw" (S4E08).