This is a simple little toy me and my friends would make as kids. It can be loaded with peas, beans or other things that would either rot or sprout into something out in nature. (don't want to pollute you know)
Step 1: What You Need
An empty toilet paper roll. (or any other cylinder you have at hand), scissors, tape,balloon and ammunition.
Step 2: Cut Balloon in Two
Cut balloon in two about where I did. You can experiment with different shapes and types of balloons.
Step 3: Putting the Balloon on the Roll.
Stand up the roll and stretch out the balloon before you put it over the one end of the roll.
Step 4: Like This, Then Add Tape.
Be sure to have a good amount of balloon for the tape to hold onto, then put on a couple of rounds with tape.
Try to get a little "nipple" on the balloon to make it easier to grab it.
Step 5: Load It
Put the bullet of your choice into the gun. Notice how the bean lays in the little "nipple" which makes it easy to grip.
Step 6: And Aim!
Aim, is not really the right word though, since it's close to impossible to get a good aim with a balloon. I guess if you really get to know your own gun, it's possible.
Warning!!!! Do NOT shoot at people with this. Depending on the balloon and shooter the bullet can give you some serious bruises, let's not mention what it would do to any eyes.
Use on your own responsibility, and be wise.