In the beginning of the film, Harry Tasker (Arnold Schwarzenegger) uses a Glock 17 2nd Generation pistol to shoot the guards pursuing him from the mansion. In the script the gun was classified as a Glock 21 .45 ACP but it was changed to a Glock 17 for the film, likely due to the larger magazine capacity. He was supposed to use the Glock 21 throughout the whole film but he instead uses a Ruger KP90.
During the bathroom scene, one of the two terrorists who follow Tasker (Arnold Schwarzenegger) attempts to kill him with a sound suppressed Makarov PM, but thanks to the camera in the fake cigarette package on the bathroom sink, he is able to see the attack coming from his glasses, and avoids the shot, and he then disarms the terrorist using it.
Steyr TMP
One of the Crimson Jihad terrorist that Tasker (Arnold Schwarzenegger) kills in the bathroom scene is armed with a Steyr TMP.
Ruger KP90
The Ruger KP90 is the standard issue sidearm of Tasker's (Arnold Schwarzenegger) association, being carried by him, Albert Gibson (Tom Arnold), and Faisil (Grant Heslov) in many scenes. Tasker notabley uses it when combating Salim Abu Aziz (Art Malik) in the bathroom and the proceeding chase through Cental Park and and the Marriot hotel.
Custom Shortened AKMS
Salim Abu Aziz (Art Malik) can often be seen using a Custom Shortened AKMS with two magazines taped together "jungle-style" as his primary weapon. It appears to have had the barrel professionally shortened to compact status, and clearly uses the hooded Norinco front sight, as well as other parts from both the Norinco Type 56 and the AKMS.
Heckler & Koch HK94A3 (chopped & converted)
When Tasker (Arnold Schwarzenegger) and several other agents capture Helen (Jamie Lee Curtis) and Simon (Bill Paxton) for interrogation, they are armed with Heckler & Koch HK94A3s chopped down and converted to full-auto fire to resemble Heckler & Koch MP5A3s. They are also seen in the hands of the SWAT team members escorting the news reporters to the terrorists in the skyscraper building.
Juno Skinner's sidearm of choice. She uses it to hold up Helen Tasker and they struggle for it, killing the driver and rendering the limousine out of control.
Another weapon of the Crimson Jihad is a Cobray M11/9 which is briefly seen in the hands of a terrosist following Aziz (Art Malik) when he goes to meet Tasker (Arnold Schwarzenegger) after him and his wife are captured by the faction.
Another weapon of the Crimson Jihad is a full size Uzi which is briefly seen in the hands of a terrosist following Aziz (Art Malik) when he goes to meet Tasker (Arnold Schwarzenegger) after him and his wife are captured by the faction.
While fighting his way throught the Crimson Jihad camp Tasker (Arnold Schwarzenegger) uses an AKM twice. One of the terrorists can also be seen stripping and cleaning one before Harry kills him.
MAC-10
While fighting their way through the terrorist camp, Harry (Arnold Schwarzenegger) hands Helen (Jamie Lee Curtis) a MAC-10. In one of the film's more humorous scenes, Helen drops the weapon down a flight of stairs causing it to go off when it hits each step, and the stray rounds score several kills.
Mk 2 hand grenade
At one point in the film, Tasker (Arnold Schwarzenegger) uses a Mk 2 hand grenade to kill several terrorists. For those wondering where this grenade came from, it was originally in the script that Juno put a grenade between Helen's legs, saying all she has to do is keep her legs closed, which Helen remarks is a problem Juno seems to have. When the two escape, he repinned it somehow for use again later. They cut this scene out of the film, causing this grenade's presence to be a continuity error. Another goof is that Tasker is shown being able to pull the pin on the grenade with his teeth, something that would be impossible in real life without suffering significant dental injury.
M72 LAW
At the end of the firefight in the Crimson Jihad camp, Aziz (Art Malik) uses an M72 LAW to try to kill Tasker (Arnold Schwarzenegger), although Tasker is able to escape the blast.
During the highway scene when the Marine Corps Harriers are destroying the trucks the Crimson Jihad and the nukes are traveling in, one of the terrorists attempts to shoot down one of the Harriers with an FIM-92A Stinger, but luckily the pilot avoids the shot, the only casualty being another terrorist who is blown out the windshield of the truck by the backblast before being run over.
M60 machine gun
Near the end of the film when Tasker (Arnold Schwarzenegger) goes to rescue his daughter Dana (Eliza Dushku) from the terrorists in a Marine Corps Harrier, some terrorists flying by in a helicoter fire a door mounted M60 machine gun modified to use a brass catcher at the aircraft, and shatter the front of the cockpit's windshield while Tasker is trying to grab his daughter as she hangs from a construction crane. The M60 machine gun had the fore end removed and the catch bag mount installed to use the brass catcher on the M60 but retained the standard buttstock and trigger group.