Anthony "Swoff" Swofford (Jake Gyllenhaal) uses two Remington M40A1 rifles in the film, first using one with a camo finish stock to train to be a Scout Sniper in Basic Traing, the second a desert camo painted model with a foam rubber sniper cheek pad. Swofford never gets to fire his rifle in combat so to make up for this, he fires his rifle into the air at the end of the film to celebrate the war's end.
The M16A2 appears numerous times in the film as the standard weapon of the U.S. Marine Corps, most notably in a scene where Swofford snaps under stress and holds Fergus (Brian Geraghty) at gunpoint with one and forces him to recite the Rifleman's Creed, then gives the weapon to Fergus and demands for him to shoot him with it, which fergus refuses to do. During the Scout/Sniper training, The Marines are also seen using M16A2s converted to fire paintballs in a dismal attempt to take out their instructor, Staff Sgt. Sykes (Jamie Foxx), one of the Marines, Fowler (Evan Jones) takes a paintball to the face in the process.
At the end of the film when the Marines fire their weapons into the air in celebration of the war's end, Alan Troy (Peter Sarsgaard) fires his M16/M203 combo into the air, and his M16 is clearly seen firing full-auto. Since an M16A2 fires in 3 round bursts, it is assumed to be an M16A3. This would also be a historical anachronism, since the M16A3 wasn't in service during the first Gulf War, however, most M16A2s in motion pictures are just full auto A1 lower receivers built up to look like A2s.
The Cobray 37mm Launcher appears in the film mounted on several Marines' M16A2 rifles, most notably Fergus and Troy's rifles. These faux-launchers take the place of the actual M203, although some genuine M203s are seen, sometimes they even switch between the two in continuity errors.
The M203 grenade launcher is seen mounted on Fergus and Troy's M16A2 rifles sometimes taking the place of the Cobray CM203 launchers used in other scenes.
The FN M249 SAW makes a few appearances in the film, most notably when the Marines are having a party to celebrate the end of the war, wherein it is one of the weapons being fired into the air. Fergus is the most notable of users to use it during this scene.
The standard used M60 at the time of Desert Storm, the M60E3, is seen several times in the film. Its first appearance is when the Marines are crawling through barbed wire in basic training, when a soldier is ordered to fire live rounds over their head. A trainee snaps and stands up and is killed by the gun. Aside from smaller appearances, the M60E3 is not seen much more until the end of the film, when several Marines are seen firing M60E3s into the air, including SSgt. Sykes.
When the Marines watch the infamous "helicopter scene" from Apocalypse Now, the Việt Cộng fighters on the screen are seen with AKs. If memory serves me right, they were using Norinco Type 56 rifles.
When the Marines watch the infamous "helicopter scene" from Apocalypse Now, one of the helicopters seen fitted with GE M134 Minigun, which a door gunner is seen firing.
The Beretta M9, the U.S. Military issued Model 92FS, appears several times in the film, seen mainly holstered in Officer's belts. This includes Lt. Col. Kazinski (Chris Cooper) when he motivates the Marines when they first arrive, one is seen in SSgt. Sykes' holster, and Major Lincoln (Dennis Haysbert) keeps one in a shoulder holster. Among the weapons seen fired into the air at the end of the film, an M9 is used by one of the Marines.
An M18A1 Claymore mine makes a rather humorous appearance in the film when Fergus asks Swofford which way the mine should be planted facing, obviously having failed to notice the words "FRONT TOWARD ENEMY" on the front of the mine, which Swofford sarcastically points out.
In the scene where the Marines are digging their sleeping holes at the border just before the start of Operation: Desert Storm, an M136 AT4 can briefly be seen among some of the Marines' gear.
Browning M2HB machine guns can be seen mounted on the Tank Commander's hatches of M1A1 Abrams tanks (in reality mocked-up British-built Centurion tanks as used in Courage Under Fire) and one is seen on a humvee in the parade when the Marines return home.
When Swofford is speaking his monologue at the end of the film, MSgt. Sykes(if you look closely on his plate carrier vest it shows Master Sargent Insignia) is seen serving in Iraq armed with a M4A1 carbine fitted with an ACOG scope and RIS foregrip. A soldier can be seen using one on Swofford's TV as well.
