Gatligator

It fires quickly and lands almost nothing at distance. The cone is wide enough that shooting one far-off enemy sprays most of the burst into empty air, so this only works pressed against something or fired into a crowd where every stray round still finds a body.

The ammo saving takes some of the sting out of the waste, but the Traveling Merchant asks a lot for a gun you will shelve as soon as a Megashark is buildable. Buy it if he wanders in early in hardmode and your ranged options are thin. Skip it otherwise.

Gatling gun plus alligator, with a barrel and chamber sculpted to match. It belongs to the same running joke as the Minishark, the Megashark and the S.D.M.G., every one of them a fast-firing gun named after something that lives in water.