Auto Crossbow From MCD.

This crossbow type will shoot arrows at a much faster rate, and it will automatically reload and fire if the use key is held down. The arrows it fires deal half the damage of a regular arrow but will deal more damage overall as of the very high fire rate.

It cannot be crafted and only found in bastion remnants and end cities.

The auto crossbow already exists in minecraft dungeons so it will be relatively straightforward to port it into the base game (I think).