Soldiers of the 25th Infantry Division "Tropical Lightning" in both Elias and Barnes' squads use M16A1s, most commonly seen in the hands of Pvt. Chris Taylor (Charlie Sheen).
MGC M16 replica
In several scenes, MGC-16 replica rifles are used in place of blank firing M16A1s. They are noted by their shortened forward assists. Most MGCs have blued magazines but they appear to have regular mags stuck in instead.
M16
Crawford (Chris Pedersen) is briefly seen using what appears to be an original M16 as it lacks a forward assist. It could also be an AR-15/SP1 rifle, but since he is not seen firing it, it is unknown.
Colt Model 653
Sgt. Elias Grodin (Willem Dafoe), Sgt. Robert Barnes (Tom Berenger), and Lt. Wolfe (Mark Moses) are armed with Colt Model 725 rifles noted by their rounded forward assists an 14.5" barrels. It is rather anachronistic to see these rifle in 1967 Vietnam, as they were not developed until the early '70s.
M1911A1
The M1911A1 is the standard sidearm for all of the NCOs and Officers in the film. It is most prominantly seen used by Sgt. Elias (Willem Dafoe) when he does tunnel rat duty and Sgt. Barnes (Tom Berenger) when he uses it to threaten a little girl in the Village to get her father to talk.
Throughout the film, several of the soldiers are seen carrying M60 machine guns while on patrol. No one is mainly listed using one more than another because in Vietnam, sooner or later, everyone had to lug the 23lb Pig around on patrol.
The Norinco Type 56 is the weapon of choice of the Vietnamese troops, many of which feature "pig-sticker" under folder bayonets. They are noted as Chinese Type 56 rifles based on their hooded front sights. Only the milled receiver variant of this rifle was actually used during the war. Towards the end of the film, both Sgt. Robert Barnes (Tom Berenger) and Pvt. Chris Taylor (Charlie Sheen) are seen using these rifles, picked up from dead Vietnamese soldiers.
M79 grenade launcher
The M79 grenade launcher is seen used by several soldiers during the film, including an unknown member of Barnes' squad.
An M72 LAW is seen strapped on top of Pvt. Chris Taylor's (Charlie Sheen) pack. Also seen used by BArnes during the final stand.
M34 White Phosphorous Grenade
A soldier is seen throwing an M34 White Phosphorous grenade (also called "Willy Pete" - slang for White Phosphorous) in one of the rice wells during the raid of the village. Sgt. Barnes also uses an M34 Grenade to destroy one of the underground tunnels, this time yelling "Willie Pete!" when he throws the grenade.
M26 "Lemon" hand grenade
M26 "Lemon" hand grenades are seen several times as the standard issue grenade of the members of the 25th Infantry.