Megashark

This is the gun that carries most ranged characters from the first mechanical boss all the way through the jungle. It fires fast enough that you stop aiming individual shots and instead hold a rough line, letting the stream drift onto the target. The ammo saving is the quiet half of its value: a stack of bullets lasts far longer than the fire rate suggests, so you can afford to use expensive ammo in it.

Accuracy is what separates it from the Uzi and especially the Gatligator. Both of those throw rounds wide, and this one keeps a tight enough cone to hit something on the far side of an arena.

The bullet matters more than the gun. Crystal Bullets turn the spray into an area weapon, which is why this pairing is the standard answer to Plantera: the shards clip the hooks while the bullets land on the body. Ichor Bullets are for anything with heavy defense, and Chlorophyte Bullets let you keep firing while you concentrate on dodging.

Do not bother upgrading from the Minishark piecemeal. Skip straight here once the shark parts and the boss are dealt with.