Cursed Bullet

The hit itself is not the point. Cursed Inferno keeps ticking through water, so this is the one damage over time effect you can count on in the Ocean, in a flooded cavern, or against anything that likes to dive under the surface. Ordinary fire goes out the second the target touches liquid.

A Crimson world hands you Ichor Bullet instead, and on raw damage output Ichor usually wins because stripping defense helps every other attack you have, not just the gun. These are the Corruption answer, and they are at their best on a fast firing weapon where the burn never has a chance to lapse. Against a heavily armored target the burn is a smaller share of your total than it looks.

The rounds glow green in flight and stay lit in the dark, so you can see exactly where your shots are landing when you fire into an unlit cave.