Projectile Goodness

I have come into possession of a trebuchet.
It’s not a very large one (the arm is only 12″ long and it uses AA batteries as weights), but it will suffice for now.
Right now, it’s being used to bombard (with partial success) my co-workers with small pieces of plastic. Much amusement ensues.
Myself and several others in the physics department are working on a project to construct a larger trebuchet, which will hopefully be used for bombarding things with water balloons. Being physics folks, we’ll try the gravity method first, but we’re looking at using a solenoid to attract an iron rod and drive the arm, so we can better tune the force to compensate for range.
Please disregard any mention in the police blotter of the local papers regarding a mad scientist with medieval siege engines. It couldn’t possibly be me. No way.