Caster Gun (3.5e Equipment)
From D&D Wiki
A caster gun is a ranged weapon that fires Caster Shells.
The caster gun can hold three shells in a rotating cylinder. Preparing the next shell in the cylinder after firing is a swift action for an unenchanted caster gun, or no action for an enchanted caster gun. Reloading all three shells takes a move action.
When an attack with a caster gun hits, the damage indicated above is inflicted, in addition to the effects of the caster shell.