M16A1s are used by various characters throughout the film. Since this film takes place in the early '70s, the introduction of the 30-round magazine is historically accurate.
M16 (SP1)
Col. Kilgore (Robert Duvall) is seen briefly holding an M16 (SP1) rifle noted by its "slab-side" reciever after the battle at Vihn Din Drop. The gun notably has an A1-style lower reciever, as evident by the fencing around the magazine, meaning this is a "franken-gun". The Use of the M16 is an error as the original M16 was never used by the US Army or any other branch of the US Military other than the Air Force. By the time the movie takes place (1970) the all M16s that were being used by the entire US Military were already replaced by the M16A1 as seen above.
When the PBR boat is taking incoming tracer rounds, Two MGC M16 replica's are shot up.
M60 machine gun
M60 machine guns are used by Col. Kilgore's (Robert Duvall) gunners during the battle at Vinh Din Drop. Clean (Laurence Fishburne) is the M60 gunner on the Navy PBR. Chef (Fredric Forrest) is seen with it briefly while taking incoming arrows from natives, but switches to the single mounted M2.
M60D
M60D machine guns are mounted on Col. Kilgore's (Robert Duvall) choppers during the battle at Vinh Din Drop.
Browning M2HB
Browning M2HBs are single and double hand mounted on the Navy PBR. Jay 'Chef' Hicks (Fredric Forrest) is the rear gunner with the single mounted M2HB (nicknamed after the band "Canned Heat"). Lance Johnson (Sam Bottoms) is the front gunner with double hand mounted M2's. While traveling on the river through the Do Lung Bridge two soldiers are seen firing an M2 trying to kill a single VC under all the dead VC bodies.
M1911A1
An M1911A1 is seen on Capt. Benjamin Willard (Martin Sheen) nightstand in hotel bedroom in Saigon at the start of the film. Lt. Col. Bill Kilgore (Robert Duvall) uses one as his sidearm throughout the movie. In a deleted scene, Col. Walter E. Kurtz (Marlon Brando) aims Willards 1911 at him when he's caged.
M79 grenade launcher
An M79 grenade launcher is used by The Roach (Herb Rice) to kill an NVA soldier hiding in the barbed wire during the scene at the Do Lung bridge. Roach had customized his with a tiger-strip paint job.
GE M134 Minigun
A GE M134 Minigun is seen door-mounted on one of the UH-1 Huey choppers during the famous raid scene. Being that the movie was filmed in the Philippines, they also supplied the helicopters which were outfitted with real guns. Since the weapons require no blank adaption to fire, all they needed was lots of blank ammunition to get the guns running.
NVA are seen using Norinco Type 56 assault rifles throughout the film, and they are also seen in the hands of Kurtz's men. It is noteworthy that this film was released in 1979 and took nearly three years to complete (thus photography started in 1976). During the 1970s, the Norinco Type 56 were not being imported into the U.S., and none were in U.S. Armorer inventories. The only reason Coppola's film had them was because they were supplied by Filipino armorers in Luzon.
Ithaca 37
Capt. Colby (Scott Glenn) carries an Ithaca 37 fitted with a heat shield and bayonet lug. In a deleted scene, he uses it to kill the photojournalist (Dennis Hopper) for taking Kurtz's picture only for Willard to throw his knife hitting him in the gut, killing him.