At that time m16's had just come out and almost everyone had that.(caliber: .223 or 5.56 NATO)
M-16
For riflemen they used an M-16 light machine gunners used an mg
Mostly motorbikes are used in Vietnam
Mostly motorbikes are used in Vietnam
The M14 and M16 were both new rifles which debuted while the US was involved in Vietnam to some extent. The M14 is the battle rifle - the M16 is an assault rifle.
Dong
The US Army's M16 was considered a "light rifle" for jungle warfare in 1963. While troops used the M14 service rifle thru-out the world, only Vietnam used the "light rifle."
The M40 rifle was introduced in 1966. It is a bolt-action sniper rifle used by the United States Marine Corps, or USMC. It is still being used. It was previously used in wars such as the Vietnam War and the Iraq War.
The Ariska was the main rifle used by Japanese soldiers in WW2
The rifle was the main gun of the Infantry man so every major battle in WW 1 the rifle was used.
Many makers have had a M21. You might be referring to a variant of the M14 used for sniping @ Vietnam era.
Union forces had privately purchased them. Rebel forces used captured repeating rifles. The repeater, was considered the "assault rifle" of the Civil War. Just as the M16 assault rifle replaced the M14 rifle in Vietnam.