Nathan Wuornos (Lucas Bryant) carries a Glock 17 as his chief sidearm throughout Season 4. "Lexie" (Emily Rose) fires the Glock to scare Jordan in "The New Girl" (S4E05). The pistol is used by Duke (Eric Balfour) when under the control of Tyler in the same episode. Jennifer Mason (Emma Lahana) takes the Glock to defend herself.
Glock 26
FBI Special Agent Audrey Parker (Emily Rose) carries a Glock 26 as her sidearm in Season 4.
SIG Pro SP 2009
In "Fallout" (S4E01), William (Colin Ferguson) acquires a SIG Pro SP 2009 from a man in the bar. "Lexie" (Emily Rose) grabs the SIG and uses it to threaten William in "Survivors" (S4E02).
In a continuity error, the SIG Pro SP 2009 used by William changes to a SIG-Sauer P226 in "Survivors" (S4E02). The "Sinister Man" (Kyle Mitchell) uses what appears to be a SIG Sauer P226 to threaten Dwight in "William" (S4E09).
Smith & Wesson 5946
Duke Crocker (Eric Balfour) continues to carry a Smith & Wesson 5946 as his chief sidearm throughout Season 4. In "The Lighthouse", Dave Teagues (John Dunsworth) is briefly seen with a Smith & Wesson 5946.
Walther P99
William (Colin Ferguson) is briefly seen carries a Walther P99 during "The Trouble with Troubles" (S4E10).
Beretta 92FS
The Beretta 92FS is used by Jordan McKee (Kate Kelton) while in a confrontation with Nathan in "Countdown" (S4E06).
Revolvers
Smith & Wesson model 10
In "Lost and Found" (S4E04), Dave Teagues (John Dunsworth) is briefly seen with a Smith & Wesson 5946 when he talks with Jordan.
Unknown Revolver
During a dream sequence, an Unknown Revolver is fired in "Lay Me Down" (S4E07).
Shotguns
Remington 870
Jordan McKee (Kate Kelton) uses a Remington 870 to stop the Nathan's car in "Fallout" (S4E01). Nathan Wuornos (Lucas Bryant) carries a Remington 870 during the rescue of Dwight in "William" (S4E09). The shotgun later in the episode is seen in the hands of Dwight.