Ammunition Unit is a term used to describe the components of a firearm that are necessary for it to function. The three crossword solutions for this term are ROUND (5 letters), Tracer (6 letters), and LOAD (4 letters). A ROUND is a bullet or projectile, Tracer is a type of ammunition that contains a pyrotechnic charge which produces a visible trail of light, and LOAD is the amount of ammunition that can be fired from a firearm at one time.