As in all the previous Lethal Weapon films, Detective Martin Riggs (Mel Gibson) carries a Beretta 92FS as his weapon of choice, albeit this time fitted with a laser pointer integrated into the grip panels.
At one point in the film, the pistol is rendered unusable when the lead villain, Wah Sing Ku (Jet Li), manages to field strip the pistol through crafty manipulation of the takedown lever although he seems to have reassembled it afterward because he is seen wielding it in the final shootout and at the end.
Smith & Wesson Model 19
As in all the previous Lethal Weapon films, Detective Roger Murtaugh (Danny Glover) carries a Smith & Wesson Model 19 revolver as his standard weapon.
OA-93
At the beginning of the film, Riggs and Murtaugh respond to a call of a man dressed in a fireproof suit wreaking havoc with a flame thrower and an OA-93.
What is interesting is that there is a small "pistol" buffer tube attached to the upper receiver of the OA-93. This feature is not part of the OA-93 design, which has a distinctive recoil assembly above the upper receiver which eliminates the need for a buffer tube with spring. Movie armorers had difficulty making the OA-93 cycle blanks, so they added the small buffer tube to the back of the gun, however the original gun doesn't have a buffer tube.
As in the previous two Lethal Weapon films, Detective Murtaugh uses a Smith & Wesson 5906 as his back-up weapon. Detective Riggs also brandishes this weapon during the encounter at Murtaugh's house.
Glock 17
During the encounter at Murtaugh's house, one of the Chinese triad gang members, Fan(George Cheung) can be seen with a Glock 17, Lorna Cole (Rene Russo) laster manages to get the weapon away from him.
Flamethrower
At the beginning of the film, Riggs and Murtaugh respond to a call of a man dressed in a fireproof suit wreaking havoc with a flame thrower, torching anything that comes near.
Colt Commander
Leo Getz(Joe Pesci) has a Colt Commander that he has acquired as he has become a "private detective". He tries to shoot a shark they caught on Murtaugh's boat before it is taken away by Riggs and thrown overboard.
Gold Cup National Match M1911A1
In several scenes, a rookie officer, Detective Lee Butters (Chris Rock) can be seen wielding a stainless steel Gold Cup National Match M1911A1 as his standard weapon.
Smith & Wesson 4506
When Leo is pulled over by a motorcycle cop for double parking the motorcycle cop is armed with an Smith & Wesson 4506
Makarov PM
Several members of the Chinese triad can be seen wielding Makarov PM pistols, most notably during the encounter in Murtaugh's house. From closer examination of the pistols, it appears that the Makarovs used by the triads were Chinese-made Norinco copies of the Makarov PM.
You think?! It would only make too much sense for chinese thugs to be using chinese made weapons.
Type 56
PLA soldiers escorting the "4 fathers" are armed with Norinco Type 56s along with a smuggler.
AKM
Several of the PLA soldiers and the General's men are armed with AKMs.
Beretta Cheetah
When Riggs & Murtaugh reveal that the money being paid to the Chinese General is counterfeit he flips out and kills one of the 4 fathers with a Beretta Cheetah before being killed by Triad members.
Several of the General's men use them as well.
Near the end of the film, a three-way gun battle erupts between the protagonists, Chinese triad members, and the private army of a corrupt Chinese General. The General's men can be seen wielding Type 56 and Type 56-1's, one of which Riggs gets ahold of to kill Wah Sing Ku (Jet Li), firing the weapon point-blank while both of them are underwater.
This is definitely either an East German MPi-KMS, or another AKM variant fitted with the East German-style folding stock. -MT2008
Is shooting the AKMS underwater impossible? -Sdawg44
Well since they actually did it in the movie, I'm assuming it is. After soaking under water so long, the powder in the bullets would be too damp to fire, so they must have submerged immediately before firing the gun. - Gunmaster45
Ammunition is fairly waterproof so the powder would be safe for a while. Any gun will fire once underwater but its unclear if it would fire full auto as is depicted in this movie. -sigger9mm