Paint pellet gun
From Halopedia, the Halo wiki
Introduction
The Paint Pellet Gun is a UNSC weapon that fires small pellets filled with paint.
Uses
The Paint Pellet Gun was used by CPO Mendez and drill instructors to train the Spartan-II's on the agricultural planet, Reach. It was used to snipe the Spartans in parade drills to teach them a lesson that things would be twisted, and unpredictable.
Service
It was probably only used in training when they were young, 6, 7, 8, 9 years old.
Speculation
It was only mentioned in one place, but it's highly possible that Mendez used them in other lessons and missions.
in Halo 3 On The Pit Map which is a traing facility there are a few of the tan colored cement walls that have what seem to be a heavy ammount of colored paint splatter in small circler pattrens these could vary well be a area of use for these weapons (Varification Needed)
Sources
Eric Nylund, The Fall of Reach, p. 47.
