Sean Penn as Sgt. Tony Meserve uses a fake XM177, built up from an SP1 Carbine. What makes it weird is the unusual flash hider/muzzle brake which is too long for an XM177, the wrong diameter and has holes on one side only (the left side).
M79 grenade launcher
Used by PFC Max Eriksson(Michael J Fox). It is notoriously seen used to blow away an incoming grenade thrown at him, which in reality did happen to PFC Max Eriksson during the Vietnam War.
M60 machine gun
Type 56 AK47
Used by the VietCong's.
Mk2/M67 hand grenade?
Used to blow up PFC Max Eriksson in the Barracks Toilets.
(I cannot remember the grenade used in this scene as i havent seen this movie for some time)