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.
Kimber Custom TLE/RL II
A Kimber Custom TLE II is drawn by an SIS officer in "The Wine of Youth" (S4E06).
Glock 17
Bosch's partner, Detective Jerry "J. Edgar" Edgar (Jamie Hector) carries what appears to be a Glock 17 as his service weapon. Other LAPD officers also armed with the Glock include Chief Irvin Irving (Lance Reddick), Lt. Grace Billets (Amy Aquino) and Sgt. Amy Snyder (Winter Ave Zoli). (The Glock 22 is the official department issue of the LAPD).
Glock 26
A Glock 26 appears to be the pistol taken out by Eleanor Wish (Sarah Clarke) in "Devil in the House" (S4E03).
Beretta 92FS
The Beretta 92FS, which was previously the department-issued service weapon of the LAPD, is seen carried by several veteran officers, including Det. Jimmy Robertson (Paul Calderon) and Det. Francis Sheehan (Jamie McShane).
Colt M1911A1
A Colt M1911A1 is seen in the hands of Det. Francis Sheehan (Jamie McShane) in "The Wine of Youth" (S4E06).
FN FiveseveN
In "Past Lives" (S4E04), an FN FiveseveN is seen used.
Colt Model 1903
In "The Wine of Youth" (S4E06) a Colt Model 1903 is found at a hit and run crime scene involving "KTK" (Monti Sharp).
Rifles/Carbines
M4A1
In "Past Lives" (S4E04), SWAT and Metro officers are armed with the M4A1 while making a raid.