The Carbuncle is a powerful Torgue-alien hybrid pistol that has ammo consumption based on the damage multiplier on the weapon. Projectiles from the weapon explode after a short pause, dealing the listed damage on the item card. As the projectiles have reduced speed, aim adjustment is required for a direct hit on small or agile enemies. Aiming at the ground around the enemy is also viable as the weapon's splash damage can cause them to flinch.
A character build that is centered around ammo regeneration is useful to keep up with the weapon's heavy ammo consumption, but pistol ammo is plentiful enough that this is not required.