Al's fancy fire flinger

This attachment is designed by the famous alchemist Alfredo Jones, created to ward off enemies and to barbeque multiple racks of ribs at the same time. As an action you target creatures in a 15 foot cone. These creatures must make a dexterity saving throw. On a failure, they take 2d6 fire damage. On a success, they take half the damage dealt. The fire flinger can hold 3 charges before needing to be refilled. It requires flammable oil and takes an action to refill.