Chain Gun

It fires faster than anything else in the game and it sprays. At any real range a large share of your shots miss a moving target outright. Chlorophyte bullets fix that by steering themselves into whatever you are aiming at, and that pairing is most of the reason the gun is good. Crystal bullets are the other answer, since the shards they shed turn a wide cone into extra hits against anything large.

It burns through ammunition faster than any other gun, though it wastes much less than the rate of fire suggests. For everyday clearing, run the Endless Musket Pouch and save the good rounds for fights that matter. On prefixes, the use time is already so low that rounding makes Rapid disproportionately effective, while Godly trades some of that speed back for ammo economy. Unreal is not available on it at all.

Anything with a huge health pool and no ability to dodge is the ideal target. The Dungeon Guardian in particular folds to it in a way it does not to most weapons, especially with crystal rounds adding extra hits on every shot.