At the beginning of the film, when a younger Caine goes outside to hang out with Pernell (Glenn Plummer) during the scene set in 1978, Pernell shows Caine his Colt Python .357 Magnum.
Colt Detective Special
Caine's father, Tat Lawson (played by Samuel L. Jackson in cameo) uses a Colt Detective Special to kill a man (James Pickens Jr.) who owes him money during the card game scene set in 1978. An interesting goof is that Detective Specials hold only five rounds, yet he fires eight times.
Beretta 92FS
After the movie shifts to 1993, the Beretta 92FS becomes a very commonly-seen gun in the film. Caine (Tyrin Turner) carries a Beretta as his sidearm throughout the movie. Berettas can also be seen in the hands of LAPD officers, one of the carjackers, and one of the drive-by shooters at the end of the film. Due to a continuity error, O-Dog's (Larenz Tate) Glock 19 turns into a Beretta when Caine uses the gun to pistol whip Chauncy (Clifton Powell).
Glock 19
O-Dogg's (Larenz Tate's) sidearm is a Gen 2 Glock 19 fitted with a Target rear sight, which he is famously seen using during the opening scene of the movie. Due to a continuity error, O-Dog's Glock 19 turns into other guns twice in the film. First, it becomes a Beretta 92FS when Caine uses it to pistol whip Chauncy. Later, when O-Dog fires at the drive-by shooters at the end, his Glock becomes a SIG-Sauer P226.
Taurus PT99 AFS
During the carjacking scene, Caine's cousin Harold (Saafir) reaches for a stainless Taurus PT99 AFS under the seat of his car. (IMFDB previously mis-identified this gun as the PT92, but the new Blu-Ray screencaps reveal that Harold's gun has the target rear sight of the PT99.)
Desert Eagle Mark VII
A-Wax (MC Eiht) uses a two-tone IMI Desert Eagle Mark VII when he, Caine, and O-Dog execute the carjackers at the takeout food stand. It is believed to be the .357 Magnum version, as A-Wax fires 10 rounds (9 in the magazine + 1 in the chamber), but the prop weapon itself may be chambered in a larger caliber, since he fires 10 rounds over the course of three takes (during which it's possible that the gun was reloaded off-camera between the takes).
Smith & Wesson Model 3000
The shotgun that O-Dogg uses during the killing at the takeout place is a Smith & Wesson Model 3000. Although the shotgun has a pistol grip that accepts a folding stock, the stock has been removed. This gun is also used by one of the carjackers.
Micro Uzi
One of the gang-bangers involved in the drive-by at the end of the film can be seen loading and then firing a pair of Micro Uzi machine pistols, using them akimbo. Due to a continuity error in the film, Ilena's cousin is also seen loading a Micro Uzi and then sticking it out the window of the car before the drive-by begins, but it changes to a TEC-9 as soon as the shooting actually starts.
SIG-Sauer P226
A SIG-Sauer P226 is used by one of the rival gang members during the drive-by shooting at the end of the movie (he uses it akimbo with a Beretta 92FS). Due to a continuity error, O-Dogg's Glock 19 becomes a SIG P226 during the drive-by when he fires back at the shooters.
Intratec TEC-9
An Intratec TEC-9 is used by Ilena's Cousin (Samuel Monroe Jr.) during the drive-by shooting at the end of the film. It is definitely an original TEC-9 and not the later TEC-DC9, because it has the sling loops on the end of the muzzle and receiver. A well-known continuity error is that when the shooter first sticks his gun out the window to fire, he has a Micro Uzi, but it changes to a TEC-9 as soon as the shooting actually starts.