After being attacked by the group of assassins in the mob, Insp. Callahan (Clint Eastwood) is inspired to take out his old pistol, an AMC Auto Mag 280 chambered in .44 AMP. When his Smith & Wesson Model 29 is kicked into a curb drain by Mick (Paul Drake), he replaces it with his Auto Mag for the remainder of the film. The production crew had a very difficult time aquiring this gun to the point where they had to contact the original designer, who had enough parts in his basement to build two guns for the film. The first was left live firing so Clint Eastwood could shoot it and accurately depict recoil while the second was converted to fire blanks for the film. The gun's serial numbers were "Clint1" and "Clint2".
It's because the gun is actually part of him. Humanzie3
Colt Detective Special
Jennifer Spencer (Sondra Locke) uses a nickel plated 3rd Generation Colt Detective Special as her weapon of choice to get revenge on the people that raped her and her sister long ago. Later in the film we see Mick (Paul Drake) use her gun to kill Police Chief Jannings (Pat Hingle).
Smith & Wesson 3000 Shotgun
Horace King (Albert Popwell, in his fourth and final role in the Dirty Harry series) uses a Smith & Wesson 3000 Shotgun with a pistol grip and a side-folding stock when showing Insp. Callahan (Clint Eastwood) his marksmanship on paper targets. Later, Mick (Paul Drake) takes this shotgun from him and uses it for the rest of the film.
Browning Hi-Power
Two of the mob assassins attempting to kill Insp. Callahan (Clint Eastwood) use Browning Hi-Power pistols. Later, Mick (Paul Drake) tries to grab his to shoot Callahan when he walks into his house unannounced.
IMI Uzi
IMI Uzi submachine guns are used by several mob assassins chasing Insp. Callahan (Clint Eastwood).
Smith & Wesson Model 10
A Smith & Wesson Model 10 is used by the leader of the robbers during the diner robbery, who is soon killed by Callahan (Clint Eastwood) and his two friends, Smith & Wesson.
Later, we see that one of Jennifer Spencer's (Sondra Locke) victims also has this pistol.
Smith & Wesson Model 19
One of the robbers during the diner robbery is seen briefly using a Smith & Wesson Model 19 revolver.
Ithaca 37
One of the robbers during the diner robbery is seen using an Ithaca 37 shotgun before being killed. One of the police that soon responds to the robbery is also seen using an Ithaca.
An M1911A1 is used by the bank robber that Insp. Callahan (Clint Eastwood) chases when he arrives in San Paulo.
Trivia: The chase scene in the film True Lies between Harry Tasker (Arnold Schwarzenegger) and Salim Abu Azziz (Art Malik) heavily resembles the chase scene in this film and may have been inspired by it.
Another is later seen in the hands of one of Mick's (Paul Drake) men.
Remington 7600
A Remington 7600 pump action rifle is seen in the hands of Mrs. Wilburn, who points it at Insp. Callahan (Clint Eastwood) and instructs him to leave her fish market after he starts beating on her husband George (Michael Maurer).
Beretta 92SB
Ray Parkins (Audrie J. Neenan) shows off her personal protection, a Beretta 92SB tucked in her waist "Mexican carry" style. It is assumed to be the 92SB because the earlier Beretta 92 variants had a butt-mounted magazine release and the Beretta 92F didn't exist yet, leaving only the 92SB.
A patrolman in San Paulo tries to fire his Colt Trooper at the M1911A1-wielding bank robber but is injured before he can fire off a shot. Later, one of Mick's (Paul Drake) thugs is seen shot in the head by Insp. Callahan (Clint Eastwood) while holding one.
Molotov Cocktail
The jocks who are insulted by Insp. Callahan (Clint Eastwood) in the elevator try to burn his car with Molotov Cocktails, one of which burns the back of his car while the other one fails to shattter. Callahan then parks his car over and uses the unbroken Molotov to burn their car and causes them to crash into the river.