I saw something like this on instructables and thats what gave me the idea. If you made the toilet paper roll balloon sling-shot comment saying "I MADE THAT" so i can give you credit.
If you build and like this please vote me up!
Ignore the image notes on this page
Step 1: Materiels
2 deflated water balloons ends removed
length 3/4in pvc pipe
bic pen tube
a really small rubberband
and a skewer or other ammo