I have an airzooka air cannon as part of my office armament, and it does an admirable job of shooting projectiles of air. However, one of my colleagues had expressed an interest in upping the ante, so we took it upon ourselves to make one using a 5-gallon bucket.
We followed the general path of the steps outlined in an instructable, though we substituted light-duty bungee cords for the elastic.
Cutting out the end of the bucket is a tad messy with all the plastic shavings. In cleaning up my clothes I employed a version of a trick we used in the navy when getting ready for an inspection — a few windings of tape on your hand, sticky-side out, does a good job at grabbing lint. Or plastic shavings.
Another deviation from the basic instructions was that since we used bungee cord, we drilled holes in the bucket for the anchor end, and zip-tied the other ends together, having removed the hooks. That also allowed us to use 3 lines.
The handle is temporarily an optics post. The bucket is just strong enough for it, so we need to add a second layer of something to shore that up and put both a proper handle on the body and a proper grip on the elastic. No metal, though, since a failure of some sort could be very bad news if this became a slingshot. We should be ready for our picnic next week.