In Day 4 of 24, former agent Jack Bauer, now working for the US Secretary of Defense, finds himself working again with CTU when a terrorist cell kidnaps the Secretary along with his daughter and a threat is made to execute him as well as launch a series of attacks on the United States.
The following weapons were used in Season 4 of 24:
Jack Bauer (Kiefer Sutherland) uses a Heckler & Koch USP Compact, chambered in 9x19mm Parabellum, throughout episodes 5-24
of Season 4, in both sound suppressed and unsuppressed form.
TRIVIA: There were only two H&K USP Compacts used by Kiefer Sutherland through the entire run of the series. This was because Kiefer is a method actor and did not like to change props. He only wore 3 real kevlar bullet proof vests through out all 8 seasons. (IMFDB thanks The Golden Closet for providing the documentation on this gun.)
Heckler & Koch USP
In "12:00pm-1:00pm" (S4E06), Jack is seen giving Secretary of Defense James Heller a Heckler & Koch USP while extracting him from the terrorist hideout.
In the beginning of Season 4's premiere "7:00am-8:00am" (S4E01), an assassin on a dirt bike derails a train and shoots a briefcase handler with a suppressed Beretta 92FS and takes his briefcase. Abdul Manesh (Matt Gallini) uses a suppressed Beretta 92FS when killing all of the co-workers of Andrew Paige(Lukas Haas). LAPD officers approach the Secretary's son Richard Heller (Logan Marshall-Green) with their standard issue Beretta 92FS in "8:00am-9:00am" (S4E02). Several assassins use suppressed Beretta 92FS's during the ambush at Felsted Security in "1:00pm-2:00pm" (S4E07). Also some suppressed 92FS's are captured and used by Jack when he's low on ammo in the same episode.
Beretta 92FS (Two Tone)
Henry Powell (Robertson Dean) uses a two-tone Beretta 92FS to threaten to kill the pilot if he does not fly his helicopter in "2:00pm-3:00pm" (S4E08).
Beretta 9000S
Tony Almeida (Carlos Bernard) uses a Beretta 9000S throughout the first half of Season 4, notably to save Jack and Audrey at Felsted Security in "1:00pm-2:00pm" (S4E07).
Glock 17
The Glock 17 is seen by many CTU teams and terrorists. Navi Araz (Nestor Serrano) uses a suppressed 2nd Generation Glock 17 to hunt down his son and wife throughout (S4E08) and (S4E10). Behrooz Araz (Jonathan Ahdout) gets a hold of the Glock 17 in (S4E10). Curtis Manning (Roger Cross) uses a 3rd Generation Glock 17 at his standard issue sidearm throughout the season. Habib Marwan (Arnold Vosloo) is seen using a 3rd Generation Glock 17 throughout the season. Also used by Tony when he arrives back at CTU after being held hostage by Mandy.
Glock 19
A CTU agent pulls a Glock 19 at a dry cleaning store during the arrest of Tomas Sherak (Faran Tahir) in "7:00am-8:00am" (S4E01). Jack Bauer (Kiefer Sutherland) also gets a Glock 19 after knocking out a CTU guard in "7:00am-8:00am" (S4E01). Omar (Tony Plana) also uses a Glock 19 when taking Audrey Raines (Kim Raver) hostage during Heller's rescue in "12:00pm-1:00pm" (S4E06). Tariq (Rene Millan) uses a suppressed Glock 19 in a confrontation with Behrooz Araz (Jonathan Ahdout) in "12:00pm-1:00pm" (S4E06). In 10.00pm-11.00pm (S4E16) FBI Special Agent Drake (Leesa Severyn) briefly draws her Glock 19 when investigating Mitch Anderson's apartment before she is shot by Nicole (Dagmara Dominczyk).
Glock 20
Jack gets a Glock 20 from another dead officer and after making a call, he hands it to Audrey telling her to space out her shots and conserve ammunition in episode 7. A closer look at the barrel looks like a 10mm Glock 20. It's also surprising that Audrey keeps her eyes open the whole time with out blinking.
A two-tone, suppressed SIG-Sauer P228 is pulled by Mitch Anderson (Ned Vaughn) in "8:00-9:00pm" (S4E14).
SIG Pro SP 2009
Head of CTU Field Ops Ronnie Lobell (Shawn Doyle) carries the SIG Pro SP 2009 as his sidearm. Ronnie is seen giving the handgun to Jack Bauer (Kiefer Sutherland) in "8:00am-9:00am" (S4E02). Jack then uses this weapon when staging a convenience store robbery in "9:00am-10:00am" (S4E03) and then in "10:00am-11:00am" (S4E04). The SIG PRO is then used by Tony Almeida after he is brought back to CTU, notably in a standoff with Mandy in "4:00am-5:00am" (S4E22).
What appears to be a suppressed Smith & Wesson 6904 fitted with a suppressor is pulled by Nicole (Dagmara Dominczyk) in "8:00pm-9:00pm" (S4E14). The 6904 appears to be the pistol pulled by Dale Spalding (Patrick Kilpatrick) in the Season 4 finale "6:00am-7:00am" (S4E24).
Walther P99
In "7:00pm-8:00pm" (S4E13), a Walther P99 is pulled by David Conlon (Tomas Arana) as he searches for Jack Bauer and Paul Raines (James Frain). He then is seen pulling it on Raines in the sporting goods store. In "4:00am-5:00am" (S4E22), Mandy (Mia Kirshner) pulls a suppressed Walther P99 on Agent Castle to hold him hostage.
Revolvers
Smith & Wesson Model 317
Dina Araz (Shohreh Aghdashloo) is seen giving a 3" stainless steel Smith & Wesson Model 317 to her son Behrooz Araz (Jonathan Ahdout) to clean up a loose end with his girlfriend Debbie Pendleton (Leighton Meester). The 617 is .22lr with an 8-round cylinder. The revolver is mainly seen in (S4E04) and (S4E05).
The Heckler & Koch MP5A2 is another weapon used by the CTU field ops team.
Heckler & Koch MP5A2's with Surefire 628 dedicated forend weaponlights can be seen at the CTU weapons center when Audrey and Jack are talking in "1:00pm-2:00pm" (S4E07).
Heckler & Koch MP5K
One of the assassins uses a Heckler & Koch MP5K during the ambush at Felsted Security in episode 7.
IMI Uzi
During the kidnapping of Secretary of Defense James Heller (William Devane) two terrorist's with IMI Uzi's shoot several Secret Service agents trying to get Heller in episode 1. Several Uzi's are seen at Secretary Hellers Rescue by approximately 5 terrorist in episode 6.
IMI Micro Uzi
Haddad Marwan (Arnold Vosloo) is seen using a Micro Uzi in the Season 4 finale "6:00am-7:00am" (S4E24).
Steyr SPP
A Steyr SPP (converted to automatic fire) was used in episode 1 by a kidnapper. A Steyr SPP is used in episode 6 by a terrorist at Secretary Heller holding location. One of the assassins uses a Steyr SPP during the ambush at Felsted Security in episode 7.
Sniper Rifles
Accuracy International AWP
Jack Bauer (Kiefer Sutherland) uses a Accuracy International AWP to kill two terrorists before they kill Andrew Paige (Lukas Haas) in episode 3. In episode 8, a sniper on a roof shoots Henry Powell (Robertson Dean) in the chest and all that is seen is a straight rifle barrel. It could have been a Heckler & Koch PSG-1 because of the straight smooth barrel but is very unlikely because of how rare this weapon is seen in movies, so I identified it as a Accuracy International AWP.
Bushmaster XM15 "V-Match"
A Bushmaster XM15 "V-Match" fitted with a scope is used by Lee Castle (Cameron Brancroft) during a prisoner exchange in "9:00pm-10:00pm" (S4E15).
Rifles
AKM
A terrorist uses an AKM to exchange gunfire with Jack during the rescue of Secretary Heller in "12:00pm-1:00pm" (S4E06).
AKMS
AKMS rifles are seen being wielded by terrorists in several of the opening episodes of Season 4. Secretary of Defense Heller (William Devane) takes an AKMS and kills 2 terrorists while trying to escape in "10:00am-11:00am" (S4E04). Jack takes one off a terrorist during the rescue of Heller in "12:00pm-1:00pm" (S4E06).
M4A1 Carbine
The M4A1 is seen used in Season 4 mainly by US Marines and CTU Tac team members. During the rescue of Secretary Heller, US Marines are seen armed with M4A1 Carbines fitted with foregrips, M68 reflex sights, AN/PEQ2A Laser Aiming Modules, and Tactical weaponlights in "12:00pm - 1:00pm" (S4E06). In "1:00am-2:00am" (S4E19), Chloe O'Brian (Mary Lynn Rajskub) uses the M4A1 to defend herself against one of Marwan's hitmen.
M16A4 Assault Rifle
Marines can be seen securing the area and shooting terrorist with M16A4 Rifle's in "12:00pm - 1:00pm" (S4E06).
Ruger Mini-14
A scoped Ruger Mini-14 is used by Jack when defending the sporting goods store in "7:00pm-8:00pm" (S4E13).
Shotguns
Mossberg 500
A Los Angeles Sheriff's Department Deputy uses a Mossberg 500 when responding to a hostage situation at the "Mercury Mart" in "10:00am-11:00am" (S4E04).
Mossberg 500 Cruiser
A mercenary (played by uncredited stunts performer Carrick O'Quinn) holds what appears to be a Mossberg 500 Cruiser on Agent Curtis Manning (Roger Cross) in (S4E10).
Mossberg 590
Another shotgun used by Jack during the sporting goods shootout in "7:00pm-8:00pm" (S4E13) is a Mossberg 590 with ghost ring sights.
Mossberg 590 Mariner
A Mossberg 590 Mariner is used by Jack and one of the sporting goods store owner in "7:00pm-8:00pm" (S4E13).
Remington 870
In "7:00pm-8:00pm" (S4E13), Jack takes a Remington 870 off a sporting goods store owner and uses during the shootout with the operatives.
Serbu Super Shorty
In "1:00am-2:00am" (S4E19), a hitman (played by stunt performer Brent Fletcher) uses a Serbu Super Shorty to open fire on Chloe in the CTU cruiser.
Other
General Dynamics M197 Vulcan
In "12:00pm-1:00pm" (S4E06), the Marines' AH-1W Super Cobra is prominently featured with its three-barreled version of the GE M61 Vulcan, the General Dynamics M197 Vulcan. The Cobra seen here is the real thing, as the production was able to secure cooperation from the United States Marine Corps and the Department of Defense.
M67 Hand Grenade
A US Marine is seen throwing an M67 hand grenade when clearing an entrance during the rescue of Secretary Heller in "12:00pm-1:00pm" (S4E06).
M26 Hand Grenade
A terrorist is seen tossing an M26 hand grenade in the direction of Heller and Jack during the rescue in "12:00pm-1:00pm" (S4E06).