Heavy Hitter is an Epicgun perk featured in Call of Duty: Infinite Warfare, exclusive to the Epic variant of the Mauler, the Mammoth. It doubles the weapon's damage, while reducing the rate of fire. This makes the weapon a two shot kill rather than a four shot kill up close, and a three shot kill at range, rather than a five shot kill, at a greatly reduced rate of fire.
"Full-auto ballistic weapon. Augmented with a unique nanofluid coolant that lets it fire 50mm Jackal rounds, albeit slower."