I don't know if this has been suggested before, but I'll give it a shot:

Basic Information:
This gun would work in similar mechanics to Scuttlebot (or the DA's charge). The gun has 3 bullets that come out at once, all at a relatively short range. There will be one bullet in the middle, one to the right, one to the left, each corresponding to where the gun was fired. Each bullet will be the size of an alchemer's at the respective star level ( 3*, 4*, 5*). The charge will cause the bullets to blow up, once they've hit something (enemy, obstacle, or crate).

Example:
http://oi46.tinypic.com/i5901y.jpg

I'll add more detail later if people like this idea~