Soon after America's large-scale involvement in Vietnam commenced in 1965 the 5.56 mm ArmaLite AR-15 rifle, later standardised as the M16, was purchased in ever increasing numbers and by the late 1960s had displaced the 7.62 mm M14 in combat units.
BMG GAU-16/A machine guns, or 7.62 mm GAU-17/A Gatling guns
A 7.62 mm PKT coaxial machine gun with 2000 rounds and a 30 mm AGS-17 automatic grenade launcher are the secondary armaments of the BTR-90.