The main weapon used by RoboCop (Peter Weller) is the "Auto 9". This is a Beretta 93R machine pistol which was heavily modified for the film, featuring a longer barrel with an enormous compensator/flash hider shaped like a casket, plastic grips, and a taller rear sight to match the raised front sight. Typically, RoboCop fires this weapon in 3-round burst mode. The fictional stats of the weapon claim it has an implausibly huge 50-round magazine.
When Clarence Boddicker (Kurtwood Smith) and his gang are asked by Dick Jones (Ronny Cox) to kill RoboCop, they are provided with an experimental military weapon being developed by OCP called the "Cobra Assault Cannon". The Cobras are actually older-specification Barrett M82 long-range .50 BMG rifles which have been dressed up extra plastic housing over the receivers and fitted with gigantic scopes (The scopes were originally supposed to show computer-generated targeting information, but this idea was scrapped due to budget constraints). The Cobra fires some type of powerful high explosive incendiary round that explodes upon impact; in the film, Clarence Boddicker memorably tests the weapon by firing it at the 6000 SUX sedan stolen by Joe Cox (Jesse D. Goins), destroying the vehicle (much to his chagrin). Anne Lewis (Nancy Allen) obtains one of these rifles and uses it against Leon Nash (Ray Wise) during the shootout at the abandoned chemical plant. After RoboCop and Lewis take out Boddicker and his gang, RoboCop takes one of the Cobra Assault Cannons (presumably, the same one used by Lewis) to the OCP office building and uses it to destroy the ED-209 Robot out in front.
Detroit police officer Alex Murphy (Peter Weller) carries the SIG-Sauer P226 9mm as his sidearm before he becomes Robocop. His partner, Anne Lewis (Nancy Allen) also uses one in the film.
(There has been some debate on RoboCop message boards over whether this gun is a P220 or a P226. It is definitely a P226 because the frame of the gun has the prominent bulges along the side, visible between the takedown switch and the decocker, which make the frame wider so that the gun can accommodate a double-stack magazine. The P220, which takes a single-stack magazine, lacks these; the sides of the receiver appear smooth rather than bulged, even from a distance.)
Clarence Boddicker (Kurtwood Smith) uses two different types of the Desert Eagle in the film. His main weapon is an IMI Desert Eagle Mark I in .357 Magnum with am elongated threaded barrel (sometimes fitted with a suppressor)). He also uses one without the extended barrel during the drug lab shootout. A stainless version is used by Dick Jones (Ronny Cox) in the climax of the film. The chrome pistol is the same weapon used in the infamous scene in which the hapless OCP executive Kinney (Kevin Page) is hamburgered whilst "threatening" the ED-209 prototype. The Desert Eagle was originally supposed to be RoboCop's main firearm, but it looked too small in RoboCop's hands once the suit was completed.
The Heckler & Koch P9S is the standard sidearm of the Detroit Police Department in the movie. Murphy uses one briefly during the highway shootout with Clarence Boddicker's men that he borrows from his partner Anne Lewis. Later on the station range, we see many police officers firing their P9s, indicating clearly that this weapon is their standard-issue.
Clarence Boddicker (Kurtwood Smith) uses a modified Remington 1100, a short-barreled semi-automatic shotgun with a heat shield to fire at Murphy and Lewis during the highway chase and then to blow Murphy's limbs off during his death scene. The conversion involves moving the action spring from behind the action to around the magazine tube behind the gas piston. This allows the the shotgun to be fitted with a pistol grip, and a telescoping stock. This shotgun was also used in Jake Speed, and The Highway Man. Full size Remington 1100's are seen in the hands of Detroit SWAT officers and a guard in the cocaine factory.
A semi-automatic civilian version of the Sterling Mark 6 Semiautomatic Carbine (recognizable by its 16" barrel, necessary to comply with gun laws in the U.S.) is seen used by the convenience store robber. It was imported for commercial sale into the U.S. during the 1980s and banned from import after 1989 (under the so-called Congressional Assault Weapons Ban, which, however, expired in the 2000s). The carbine is fired semiautomatic throughout the robbery and Robocop renders this weapon useless by bending the barrel under the receiver of the gun, a moment which reveals an obvious mistake: for Murphy to bend the barrel, the guy holding the gun would have to be at least that strong as well.
During the Nightclub scene, RoboCop arrests Leon Nash (Ray Wise) who pulls out an LAR Grizzly, a variant of the M1911A1 chambered in .45 Winchester Magnum with a barrel protruding past the slide. Sal's (Lee de Broux) bodyguard (Allan Graf) in the drug lab also uses a LAR Grizzly pistol.
When Emil Antonowsky (Paul McCrane) robs the gas station he threatens the clerk with an Ingram MAC-10 fitted with a custom flash hider and a modified folding stock. One of the same MAC-10's was also used on an episode of Miami Vice.
Mossberg 500 Bullpup shotguns are used by the Detroit SWAT teams, seen during the standoff at City Hall and when the police open fire on RoboCop at the OCP building.
Another weapon used by the Detroit SWAT members is the Steyr AUG assault rifle. It's used seen when SWAT is ordered to open fire on RoboCop at the OCP building. When the SWAT members advance on RoboCop, their AUG's are held sideways to eject the brass cartridges downwards. Apparently, these are loaded with high-penetration rounds, because they can somehow damage Robocop, whereas he is impervious to the AK rounds fired at him in the cocaine factory.
The Franchi SPAS-12 is used by one of Sal's men during the drug lab shootout and by at least one SWAT officer during the standoff at the Detroit City Hall.
Boddicker's crew uses several Remington 870 shotguns, all of which have folding stocks. They appear to be standard 'Police Magnum' variants, though at least one has an extended magazine tube.
Leon Nash (Ray Wise) uses an Ithaca 37 with pistol-grip and extended magazine tube during the van chase with Lewis and Murphy. He switches to a Remington 870 in the warehouse (presumably using Joe Cox's 870), while Emil Antonowsky (Paul McCrane) uses the Ithaca.
Steve Minh (Calvin Jung) wields a Mossberg 500 Cruiser with a distinctive sling swivel at the front throughout the movie, notably in the drug lab shootout.
The Enforcement Droid 209 is armed with large caliber cannons and missile launchers. The cannons are used on the hapless executive Kinney and the missiles are seen fired at RoboCop.
