The rifle in my Avatar is an M14, carried one my entire time in the Marine Corps, from 1964 to 1968. The photo was taken in 1966 on a roadside mine sweep on the road to Hill 41 where is was assigned to.
Never saw an M16 the entire time I was in the Corps, they didn't start issuing them to the Marines until after I left the Nam and they had none in Camp Lejune nor Puerto Rico whee I assigned for two years afterwards.
M14 was an excellent battle rifle, when I qualified with it in Boot Camp part of the course had you qualify with it at 500 meters at a target with a bullseye less than the width of a garbage can lid. I had 6 out of 10 in the bullseye. This was with iron sights, not a scope.