You receive a +4 to all attack and damage rolls made with firearms.

When taking the attack action, you may make an extra attack with a firearm you are holding as a bonus action.

Collateral Bullets: 

Your bullets now penetrate enemies, when you hit an enemy with a firearm attack. You may roll to hit for the next creature in line of the target up to 100 feet. On hit the second target takes damage equal to the first.
Upon a critical hit on the first target, the second target it automatically hit. Upon a critical hit on this second target, the second target receives damage equal to a normal critical hit plus the damage dealt to the first enemy.