The following weapons were seen in the film Saw:
Smith & Wesson Model 686
A Smith & Wesson Model 686 is found lying on the floor next to the dead body (Tobin Bell) in the room, Dr. Lawrence Gordon (Cary Elwes) is given one bullet and is told he has to kill Adam if he wants to see his family again, he ultimately ends up wounding Adam in the shoulder with the revolver.
Wilson Combat "Protector"
A two-tone Wilson Combat "Protector" is used by Zep Hindle (Michael Emerson) in the gunfight with Detective Tapp, it is also briefly used by Alison Gordon (Monica Potter) when she obtains it after being held hostage by Zep, Adam (Leigh Whannell) also briefly picks it up after killing Zep and aims it at Jigsaw but gets shocked by remote and drops it.
A Beretta 92FS is used by Detective Tapp (Danny Glover) throughout the latter portion of the film. He uses it during the gunfight with Zep Hindle (Michael Emerson), at the Gordon's apartment, and later when he pursues Zep through the sewers.
Beretta 92FS Inox
During the warehouse flashback, an Ithaca 37 is used by both Detective Tapp (Danny Glover) and then by Detective Sing (Ken Leung) who both hold it on Jigsaw (Tobin Bell) before he escapes. After Tapp is wounded, Sing pursues Jigsaw with the Ithaca, and manages to shoot him in the back with it, before he is killed by a shotgun trip-wire trap.
12 Gauge Double Barreled Shotgun
While pursuing Jigsaw (Tobin Bell), Detective Sing (Ken Leung) is killed when he steps on a trip wire that is connected to four loaded 12 Gauge Double Barreled Shotguns that are mounted on the archway above him.
When the camera zooms in on one of the shotgun's triggers, it turns into that of a Winchester 1300's.