Full-Chamber Volley

When you take the Attack action and make an attack with a firearm, you may choose to expend all remaining ammunition in the firearm’s magazine (maximum 6 rounds) to make one Full-Chamber Burst attack.
Make one attack roll. On a hit, the attack deals damage equal to the firearm’s normal damage multiplied by the number of rounds expended. You add your ability modifier to the damage only once.
After the attack, you gain 1 level of exhaustion. All ammunition spent is consumed whether the attack hits or misses.