These rubberband guns are really cool, and also very reliable. I've made a single and double barrel version, they hold 8 and 16 rubberbands respectively. Unlike most rubberband guns I've seen, these don't shoot all the ammo off at once, instead a special trigger allows you to shoot them off one at a time. The trigger uses a unique device called an escapement, it allows the sprocket to only move one click at a time. The trigger also has a rubber band pulling back on it to aid in loading the gun. The gun is fairly simple, and loading it is simple too. Just put rubberbands on from BACK to FRONT(order is important), then click the wheel backwards to continue loading the rest of the gun in the same manner. It's really fun to use and has pretty good range and accuracy.
Warning! don't try to make a quad-barrel version of this gun. I made one and when I pressed all the triggers it blew up! It was so awesome!!!!! but probably not all that safe.
If anyone wants instruction (although the pictures are almost instruction enough) tell me, and maybe I'll get around to putting some up.