Deputy U.S Marshal Raylan Givens and nearly all of the other US Marshals in Season 3 carry the full size Glock 17 as their sidearms, including Chief Deputy Art Mullen (Nick Searcy) and Deputy Marshal Tim Gutterson (Jacob Pitts).
Glock 17 (Two tone slide)
A suppressed Glock with a stainless slide is seen used by Robert Quarles (Neal McDonough) at the beginning of "Watching the Detectives" (S3E08). The handgun is later found by Winona in the episode.
Glock 19
In "Cut Ties" (S3E02), what appears to be a Glock 19 is seen as the sidearm of Assistant Director Karen Goodall (Carla Gugino). A Glock 19 also appears to be used by Layla (Maggie Lawson) in "Thick as Mud" (S3E05).
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. Throughout the series, he is seen carrying it in the back of his waistband. Raylan is seen firing his Glock through a dead body in "Thick as Mud" (S3E05).
In "Harlan Roulette" (S3E03), a nickel Beretta 85F is pulled on Devil in a standoff. Boyd is later seen carrying the pistol.
Beretta 8000L Cougar
In "Thick as Mud" (S3E05), Dewey Crowe is seen holding up various establishments while armed with a Beretta 8000L Cougar.
Browning Hi-Power
In "Harlan Roulette" (S3E03), a Browning Hi-Power is pulled by Jimmy (Jesse Luken), one of Boyd's men in a standoff. In "Loose Ends" (S3E09), Errol (Demetrius Grosse) uses the Browning.
Colt M1911A1 (Nickel)
In "The Gunfighter" (S3E01), Fletcher 'The Ice Pick' Nix (Desmond Harrington) is carrying a nickel M1911A1 that he uses to play a drawdown game with his victims. Raylan is also seen with the pistol in the episode. Boyd Crowder (Walton Goggins) pulls a nickel M1911A1 in a confrontation with Devil in "The Devil You Know" (S3E04).
CZ 75B
A CZ 75B is pulled by Wally Beckett (Eric Ladin) in "Harlan Roulette" (S3E03).
EKOL Tuna
Throughout Season 3, Robert Quarles (Neal McDonough) is seen carrying what appears to be a stainless FIE Titan that he keeps concealed in an arm anchor. Upon closer inspection, the pistol is actually a blank firing replica known as the EKOL "Tuna". It can be identified by its lack of side mounted external extractor, the pin in the slide which is the pivot for the top mounted extractor, the ribbed barrel and the blast porting holes part way down the barrel. He is first seen using it in "The Gunfighter" (S3E01). In a later episode, he says that he got the idea for it because he was forced to watch Taxi Driver when he was a kid. He also mentions that the rig has to work 100% of the time, because if it jams, he's screwed. In "Coalition" (S03E12), he mentions it is loaded with .32 hollow-points.
EKOL Grizzly Special 99 (Blank Fire Only)
In "Loose Ends" (S3E09), Tanner Dodd (Brendan McCarthy) is seen carrying a small compact pistol which appears to be an EKOL Grizzly Special 99, a blank-fire only pistol.
In "Harlan Roulette" (S3E03), a SIG-Sauer P226R is pulled in a standoff. In "The Devil You Know" (S3E04), the prison guard Ash (Todd Stashwick) is seen holding the SIG when helping Dickie Bennett escape. Ash's SIG appears to have an extended barrel.
Walther PPK replica Kimar "Lady K"
In "Cut Ties" (S3E02), Terry Powe (Frank John Hughes) is seen using a Kimar "Lady K" an 8mm blank fire only Walther PPK replica. Art Mullen is also seen holding the weapon.
Revolvers
Colt Python
In "The Devil You Know" (S3E04), Johnny Crowder (David Meunier) is seen pulling a stainless Colt Python on Devil.
Ruger GP100 (Stainless)
In "Harlan Roulette" (S3E03), Glen Fogle (Pruitt Taylor Vince) is seen taking out a Ruger GP100 revolver and forcing one of his men to play a different version of Russian Roulette that he calls "Harlan Roulette".
Kimar Competitive
In "Coalition" (S3E12), Arlo Givens (Raymond J. Barry) pulls a revolver on Ava. This appears to be a 4" variant of the blank fire only Kimar "Competitive" revolver.
Smith & Wesson Model 30
Wynn Duffy (Jere Burns) is seen holding a Smith & Wesson Model 30 during a conversation in "Measures" (S3E11). In the Season 3 finale "Slaughterhouse" (S3E13), Raylan is seen holding Duffy's revolver and making him play "Harlan Roulette" with it.
In "The Devil You Know" (S3E04), Ellstin Limehouse (Mykelti Williamson) is armed with a 12 Gauge Double Barreled Shotgun when confronting Dickie Bennett. One of the women sent to commit a robbery is armed with a sawed off shotgun as well in "Loose Ends" (S3E09).
Ithaca 37 Nickel
In "Guy Walks Into A Bar" (S3E10), Lindsey Salazar (Jenn Lyon) is seen taking out an Ithaca 37 with a nickel finish, pistol grip and extended mag barrel when Raylan confronts Quarles.
Mossberg 500AT Cruiser
A pistol-gripped Mossberg 500AT is seen used by Errol (Demetrius Grosse) in "The Devil You Know" (S3E04). Dickie Bennett (Jeremy Davies) is later seen in the episode with the shotgun.
Mossberg 500
In "Watching the Detectives" (S3E08), a Mossberg 500 is confiscated from Raylan's car by Lexington PD detectives.
Mossberg 590A1 (Short Barrel)
In "When the Guns Come Out" (S3E06), Tanner Dodd (Brendan McCarthy) is seen using a Mossberg 590A1 shotgun fitted with a saddle shell holder and heat shield when entering an Oxy clinic.
Remington 870
A Remington 870 with black furniture is used by one of the women sent to commit a robbery in "Loose Ends" (S3E09). In "Coalition" (S3E12), Robert Quarles is seen using one to blow smoke through, mimicking a scene from Platoon.
Remington 870 (Short Barrel)
The convenience store owner is seen pulling a short barrel Remington 870 when Dewey tries to hold up the store in "Thick as Mud" (S3E05).
In "Guy Walks Into a Bar" (S3E10), Shelby (Jim Beaver) holds a Winchester Model 1897 shotgun on the Harlan County deputies who attempt to plant drugs in his pickup.
Other
Gunrack
A gunrack containing several rifles is seen in Fogle's pawn shop in "Harlan Roulette" (S3E03).