Water balloon ballista

[ChrisH]

Originally Posted by Tytus Gerrish

make a crossbow. it's hard to make somthing better than that

Nobody has suggested the perennial favorite, the "cone cannon". A funnel and two lengths of surgical tubing (length varies by desired range) are all you need. Poke a couple of holes near the edge of the funnel, tie on the surgical tubing, a couple of friends to hold the ends of the tubing and you're ready to launch. With a little work you can get the accuracy pretty good too.