In the rare instance where a gas-powered potato gun or a pump-action slingshot may be considered “overkill,” might I suggest the less-than-lethal Bungee Bazooka?
Built from four-inch PVC piping, therapy resistance tubing, with various fasteners and hardware, this shoulder-fired slingshot can launch a bevy of projectiles–from custom-built Styrofoam darts and tennis balls to eggs and assorted fruits and vegetables.
Seamster, the bazooka’s creator, has posted step-by-step directions for building your own over at Instructables.