Several LAPD officers and detectives carry the Beretta 92FS as their sidearm, including Detective Sammy Bryant (Shawn Hatosy), Detective Daniel "Sal" Salinger (Michael McGrady), Detective Nate Moretta (Kevin Alejandro), and a number of other officers. This weapon is on the LAPD approved carry list.
Smith & Wesson 5906
Officer John Cooper (Michael Cudlitz) carries a Smith & Wesson 5906 (as evidenced by its double stack frame) as his duty sidearm. This weapon is on the LAPD approved carry list. In "Failure Drill" (S3E09), Adams is seen firing a S&W 5906 (instead of her usual 3913) on the range.
Glock 22
Officer Ben Sherman (Ben McKenzie) carries a Glock 22 as his sidearm. Officer Chickie Brown (Arija Bareikis) also uses a Glock 22 as her sidearm, although her weapon is fitted with a Surefire X-300 tactical light. Detectve Josie Ochoa (Jenny Gago) also carries the Glock. In several episodes, notably the 7th of the season, "Sideways", Officer Bill "Dewey" Dudek (C. Thomas Howell) carries a Glock 22, using it during a felony stop in lieu of his Beretta 92FS. He appears to have switched from the Beretta to the Glock after returning from rehab and going back on patrol.
Smith & Wesson 3913
Detective Adams (Regina King) carries a Smith & Wesson 3913 as her duty gun. In "Failure Drill" (S3E09), she is notably seen using it to bring down an active shooter with a "failure drill", hence the title of the episode. This is despite having been seen using a S&W 5906 on range earlier in the same episode.
Smith & Wesson Model 66
Det. Sammy Bryant is seen threatening a gang member with what appears to be a Smith & Wesson Model 66.
Raven Arms MP-25
A Raven Arms MP-25 compact pistol is seen in the opening credits of each episode.
Colt Detective Special
In "Code 4" (S3E04), Ben finds a Colt Detective Special revolver in a restaurant owner's possession. He advises him to discard of it because the serial number is scratched off, but allows him to keep it for protection until he can purchase a legal weapon, which proves to be a bad decision.
SIG-Sauer P226
After dropping his AK-47 and fleeing on foot, the outstanding bank robber (Thom Williams) in Season 3's premiere "Let it Snow" (S3E01) commits suicide with a SIG-Sauer P226.
Kimber Custom TLE II
In the season finale "Graduation Day" (S3E10) an officer can very briefly be seen carrying what appears to be a Kimber Custom TLE II while in pursuit of an armed suspect.
Shotguns
Remington 870
Several LAPD officers are seen using Remington 870 shotguns, which is the standard issue shotgun for the department. They are often seen in the shotgun racks of the police cars.
Assault Rifles
Colt M4A1
In "Punching Water" (S3E02), Metro officers are armed with Colt M4A1s as they raid the home of a gang member when searching for an AK-47 used in a murder.
AKM
An AKM is used by one of the three bank robbers in Season 3's premiere "Let it Snow" (S3E01).
AKMS
An AKMS is used by one of the bank robbers in Season 3's premiere "Let it Snow" (S3E01).
AK-47
A gang member uses an AK-47 to commit a drive-by shooting in "Punching Water" (S3E02). Police officers later seize the weapon when they raid the home of another gang member who had been hiding it.
Colt M16A2
In "Failure Drill" (S3E09), an active shooter is seen firing with an M16A2 fitted with an ACOG scope.
Submachine Guns
Intratec TEC-9
An Intratec TEC-9 is seen on the ground next to a slain bank robber after Sherman takes him down in "Let it Snow" (S3E01).
Other
X26 Taser
Officer John Cooper uses an X26 Taser to subdue a suspect in "Discretion" (S3E03) after the suspect throws Sherman through a window.