Detective Hieronymus "Harry" Bosch (Titus Welliver) continues to carry a Kimber Custom TLE II as his service weapon. The Kimber is the pistol author Michael Connelly specifies as Bosch's LAPD sidearm in his later novels.
Glock 17
Bosch's partner, Detective Jerry "J. Edgar" Edgar (Jamie Hector) carries what appears to be a Glock 17 as his service weapon. (The Glock 22 is the official department issue of the LAPD). It's seen next to Woody Woodrow's corpse in "Right Play" (S3E07).
The Beretta 92FS, which was previously the department-issued service weapon of the LAPD, is seen carried by some officers and veteran detectives in Season 3, notably Det. "Crate" Moore (Gregory Scott Cummins).
SIG-Sauer P226 E2
A SIG-Sauer P226 E2 is used by Capt. Dobbs briefly in "God Sees" (S3E03).
Colt Model 1903
A compact pistol that resembles a Colt Model 1903 is used by the Koreatown Killer throughout the season.
Revolvers
Colt Detective Special
Detective Jerry "J. Edgar" Edgar (Jamie Hector) pulls what appears to be a nickel plated, third generation Colt Detective Special out of an ankle holster.
Submachine Guns
Heckler & Koch MP5A4
Heckler & Koch MP5A4s are seen with Mexican Federal Police Grupo de Operaciones Especiales in "Clear Shot" (S3E09).
Shotguns
Remington 870
The Remington 870 also is used by LAPD officers. One is seen hanging on the wall in LAPD's Hollywood Station in "Clear Shot" (S3E09).
Benelli M3 Super 90 Shotgun
A Benelli M3 Super 90 Shotgun is carried by an LAPD officer during a search in "Aye Papi" (S3E08).
Rifles/Carbines
Colt M16A2
A Colt M16A2 is seen in the photo of a female soldier in "The Four Last Things" (S3E02).
Colt M4A1
Colt M4A1s are seen in photos of Green Beret commandos in "The Four Last Things" (S3E02) and in "God Sees" (S3E03). Some LAPD officers are armed with M4A1 carbines while making a search in "Aye Papi" (S3E08) and in "Clear Shot" (S3E09).
Daniel Defense M4A1
What appears to be a Daniel Defense DDM4 "M4A1" in an OD finish is seen in a pickup bed in "God Sees" (S3E03).
SIG-Sauer SIG556 SBR
What appears to be a SIG-Sauer SIG556 SBR is seen in the back of a truck in "God Sees" (S3E03).