this is a penny gun I found in a book called Mini Weapons of Mass Destruction. it will shoot a good 40-80 feet!
Step 1: Supplies
toilet paper roll
pennies(or anything small)
Step 2: Make It
what you'll need to do is to snip the neck off of the balloon and wrap it around the toilet paper roll so there's none hanging off. also, if you want, you can wrap rubber bands around the neck so the balloon doesn't snap off.
Step 3: GET SHOOTN'!
what you do is put the penny/projectile in the tube and pull back the balloon and the penny and let go.
Step 4: The Aftermath
this is a picture of the aftermath of me shooting pencils at this cardboard box at about 10 feet