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.
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.
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.
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.
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.
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.
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.
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.
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.
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.