Looks interesting! Odd combination of an A2 lower and an A1 upper, but still looks neat.
Those are my suits and if I remember, for the shot above, they where using some type of "air-soft" replica firearm. I'll ask the propmaster when we start back up.
The M16 round is designed to tumble on impact for greater wounding. One of the problems in a jungle, lots of vegetation to mess up the flight of the bullet.
Looks like the stock and handguards...,and the grip
From the pictures it looks like an WE M16A1 upper atleast (the cut underneath the rear sight is distinguishable, not positive though.) I think they may have changed some parts out, ie grips, buffer, stock. I just realized the lower is an A1 as well with A2 parts. (Profile of support underneath the buffer)
Love the Matt Mason poster Had a whole collection during my childhood!