The Beretta 92FS appears as the main service pistol of all LAPD officers.
Beretta 92FS Compact
A stainless steel Beretta 92FS Compact is used by drug smuggler in S03E19 to threaten an informant.
Desert Eagle
A stainless steel Desert Eagle is used by Kilo in S04E17 amd Buck Winters in S05E11.
Glock 19
A Glock 19 is used by some of the FBI Agents and it is used by Don in the season 6 finale "Cause and Effect" (I'm saying it is the season 6 finale because i am leaving room for the unknown) where it is stolen and used in a series of vilgilante murders.
Glock 23
FBI Special Agent Don Eppes' (Rob Morrow) and FBI Special Agent David Sinclair (Alimi Ballard) both carry Glock 23's as their sidearms. If you look carefully in the episodes the slide is too short and so is the frame. Also in Season 4 episode 4 during the standoff in the elevator it is clearly marked as a Glock 23.
Glock 27
FBI Special Agent Nikki Betancourt and former Agent Megan Reeves' main service pistol is a Glock 27 .40 S&W caliber pistol.
Heckler & Koch P7M8
Used by kidnapper in S01E05.
Heckler & Koch P7M13
Used by kidnapper in S02E02.
Heckler & Koch USP
A California Bureau of Investigation agent is armed with a two-tone Heckler & Koch USP in S03E12.
SIG-Sauer P226
FBI Special Agent Colby Granger's initial service weapon is a SIG-Sauer P226 before changing to the Springfield Armory Custom TRP and then finally to the Smith & Wesson PC 945.
SIG-Sauer P228
Special Agent Ian Edgerton (Lou Diamond Phillips) carries a SIG-Sauer P228 as his service pistol. Special Agent Nikki Davis (Sandra Lindquist) of the BATF commits suicide with her P228 in the episode "Guns and Roses".
Smith & Wesson PC 945
FBI Special Agent Colby Granger switches to a Smith & Wesson PC 945 with a two tone slide. Agent Granger switched to this pistol in season 5 episode "Trouble in Chinatown" using it to gun down a shooter while waiting on his takeout food with Agent Sinclair. Possibly a personal side arm.
Springfield Armory M1911
Used by Till's Uncle (a.k.a. DB Cooper) in season 6 episode "Old Soldiers".
Springfield Armory Tactical Response Pistol
FBI Special Agent Colby Granger's main service pistol is a .45 ACP Springfield Armory Tactical Response Pistol, which indicates he is SWAT/HRT (Hostage Rescue Team) qualified, since only SWAT/HRT qualified FBI agents are authorized to carry that weapon on duty.
Revolvers
Single Action Army
A Single Action Army with a 5.5" "Artillery" barrel is used by a disgruntled rancher in S02E09. Analyzing the other frames of the current and proceeding scene, the weapon has a nickel or similar finish with wood grips.
Smith & Wesson Model 66/67
Used by Russian roulette players at the beginning of S06E03.
Smith & Wesson Model 625
Used by suspect to commit suicide in S02E12.
Smith & Wesson Model 659
Used by kidnapper when holding the little girl hostage in S01E05.
Submachine Guns/Machine Pistols
FN P90
Several FN P90's appear being used by a Mexican death squad in S03E14, Chinese thugs in S05E13, and bank robbers in S06E02.
Glock 18C
Used by Ella Pierce in S04E08 to fire on FBI agents. Unsure whether this is true Glock 18C or converted Glock 17 as there is no clear view of the slide.
Heckler & Koch MP5A2
Several Heckler & Koch MP5A2's, fitted with Surefire dedicated forend weaponlights, appear being used by several FBI Special Agents in tactical gear before the switch to the MP5A3 w/RIS described below.
Heckler & Koch MP5A3
Several Heckler & Koch MP5A3's appear being used by several FBI Special Agents in tactical gear and private security guards. The Agents' MP5A3's are fitted with RIS handguards mounting vertical foregrips & Surefire Universal weaponlights. Davis can be seen using one that also features a UMP-style folding stock.
A Heckler & Koch UMP appears being used by the female bank robber in S06E02.
IMI Micro Uzi
Used by domestic terrorists in S04E08.
IMI Uzi
Used by Ella Pierce in S04E08.
Ingram MAC-10
A MAC-10 is used by school shooters in S02E19 and domestic terrorists in S04E08.
Steyr SPP
A Steyr SPP is used by counterfeiters/armed robbers in S01E07 and a Chinese thug in S05E13. It is modified to fire full-automatic in lieu of using the Steyr TMP.
Shotguns
Daewoo USAS-12
Used by Operation Condor assassin in S02E05.
Mossberg 500 Tactical
Used by Colby Granger in S06E12 in the final shootout.
Serbu Super Shorty
Used by the Charm School Boys in SO1E02
Assault Rifles
AKMS
An AKMS is used by an armed robber in the climatic firefight in S02E20.
Colt Model 603
The Colt Model 603 is commonly referred to as the M16A1. An M16A1 rifle fitted with A2 handguards was used by a religious fanatic in S03E12.
Colt Model 733
A Colt Model 733 was used by a corrupt BATF agent in an armed robbery attempt at the end of S02E20.
Colt Model 945
Used by kidnapper to provide sniper fire against the FBI in S03E17. It is mocked up to look like a Colt Model 945/KAC SR-25.
Colt Model 977
The Colt Model 977 is commonly referred to as the M4A1 carbine. It can be seen being used by FBI/FBI SWAT agents in tactical situations, fitted with various accessories such as RIS foregrips, Surefire Universal weaponlights, and C-More & EOTech red dot sights.
Heckler & Koch G36C
A Heckler & Koch G36C fitted with a RIS foregrip is used by an Asian gang member during the rescue of Colby Granger and Dwayne Carter in S04E01. Also used by a bus hijacker in SO5E12.
Kel-Tec PLR-16
Used in S03E17 by the main antagonist as he is about to kidnap his target, a little boy.
Norinco Type 56-1
A Norinco Type 56-1 is used by a disturbed parent to threaten LAPD/FBI in S02E12.
Valmet M76F
A Valmet M76F is used by an armed robber in the climatic firefight in S02E20.
Zastava M92
Used by an armed robber in the climatic firefight in S02E20.
Battle Rifles
BNT-35 (Fictional)
Team deals with this hazardous weapon in season 6 episode "Arm in Arms" It seems to have n SL8 stock, what may be a 20-round M16 magazine, and a vague XM8/SCAR resemblance.
Springfield Armory M1A
Used by the sniper in S06E01 to shoot at the FBI agents in the park.
Sniper Rifles
Accuracy International AE
Used by Charlie Eppes in S01E09 to learn the human response after firing a sniper rifle.
Remington Model 700PSS Sniper Rifle
A Remington Model 700PSS is used by Ian Edgerton in the episode "Toxin" to kill the Private Investigator stalking a potential witness.
Remington Model 700SPS
Used by David Sinclair and another agent to provide sniper cover during the climactic firefight in S04E08.
Heavy Weapons
RPG-7
Used by gangsters in the escape scene in season 4 episode "Trust Metric"