In 1969, an M16A1 is used by Pvt. Luc Deveraux (Jean-Claude Van Damme) while in Vietnam. Deveraux uses his bayonet-fixed M16A1 rifle to kill Sgt. Andrew Scott (Dolph Lundgren) by bayoneting and shooting Scott numerous times (while at the same time, Deveraux is shot by Scott's M1911A1 pistol). A number of US solders were seen armed with M16A1 rifles and M16A1 rifles fitted with M16A2 handguards when the film shifts to 1992.
Heckler & Koch SP89
What appear to be Heckler & Koch MP5K submachine guns fitted with laser sights are used by GR44/Luc Deveraux, GR13/Sgt Andrew Scott, and GR55 (Tommy "Tiny" Lister) when investigating the breaking onto the base by reporter Veronica Roberts (Ally Walker). From closer examination, the MP5Ks were in fact SP89 pistols made to look like MP5Ks.
Desert Eagle Mark I
The Desert Eagle Mark I is the sidearm used by the Universal Soldiers, including GR44/Pvt. Luc Deveraux (Jean Claude Van Damme) and GR13/Sgt. Andrew Scott (Dolph Lundgren). The Desert Eagles used by the UniSols were chambered for the .357 Magnum round and fitted with laser sights under the handgun's barrel. Their Desert Eagles are fitted with suppressors during the mission during the opening hostage situation.
M60 Machine Gun
The M60 is used by Sgt. Andrew Scott/GR13 (Dolph Lundgren) during the motel shootout and also in the Prison Bus escape.
M14 Rifle
The M14 is seen in the hands of a US soldier at the beginning of the film.
M1911A1
An M1911A1 is used by Sgt. Andrew Scott (Dolph Lundgren) in the Vietnam scenes at the beginning of the film.
Smith & Wesson Model 39
Luc Deveraux (Jean Claude Van Damme) takes a Smith & Wesson Model 39 pistol from the deceased Prison Bus driver and uses the handgun to shoot GR74 (Ralf Moeller) in the UniSol truck after the UniSol truck rammed the Prison Bus and was pushing it into the Grand Canyon.
CETME
CETME rifles are used by the Hoover Dam Terrorist members.
Sten Mk V
A Sten Mk V SMG is seen in the hands by one of the Hoover Dam terrorists that is taken by GR44.
Heckler & Koch SR9(T)
A SWAT sniper is seen with an Heckler & Koch SR9(T) fitted with a Starlight scope during the Hoover Dam hostage situation.
Armsel Striker/Protector shotgun
An Armsel Striker/Protector automatic shotgun is used by UniSol GR74 (Ralf Moeller) during the attack on the Motel.
Beretta 92FS
The Terrorist leader (Thomas Rosales Jr.) pulls his Beretta 92FS when UniSol GR74 (Ralf Moeller) appears as an Electrician at the Hoover Dam. Looking at the picture of the screenshot, I would say that's a Taurus PT92 because of the Stainless Steel guide rod for the slide.
Beretta 92FS Inox
Colonel Perry (Ed O'Ross) is seen armed with a Beretta 92FS Inox pistol.
Double Barrel Shotgun
Luc Deveraux takes his parents' shotgun to confront GR13/Sgt Andrew Scott but doesn't use it.
Heckler & Koch P9
Although he'd been shot multiple times, UniSol GR74 (Ralf Moeller) still is able to pull a Heckler & Koch P9S from his tool box to use on the terrorists. One of the Universal Soldier project technicians also is seen pulling out a Heckler & Koch P9 from the weapon racks after GR13/Sgt. Andrew Scott (Dolph Lundgren) re-entered the UniSol truck and announced that he "relieved" Col. Perry of his command.