UPDATED: New gun design and instructable steps, 08 april
Minor Update, 12 april: Ive redesigned the firing levers to stop misfires. The changes are very small but important. The very last section has a photo of the modifications.
I agree with the comments saying the gun was too bulky. Ive remade it into a much more compact and powerful design. The first few steps are the same, but theres more ones been added to show the new design. Ive also got a video of the gun firing.
I will begin this with the obligigatory "my first instructable etc....". With that out the way, onto the gun. (by the way, I know my username is spelled wrong).
This gun holds 8 shots, and will fire them as fast as you can pull the trigger. It can fire several types of connector. Using two bands per shot, it fires about 30-40 feet, though It has the potential for much more.
It does not require many "exotic" parts, however you do need quite alot of bands. I needed 19: 16 for the barrel, 1 for the barrel spinner, and 2 for the trigger return mechanism.
The basic idea is that the barrel holds the 8 shots in a ring. The barrel is tensioned by a band which makes it rotate betweeen each shot. When you pull the trigger, a level flicks one shot out of the barrel, and at the same time moves a ratchet which advances the barrel one "click", lining up the next shot. This mechanism can work very quickly- I can fire off all 8 shots in under two seconds.
Note: If you fire this at hard surfaces, it tends to break parts off the ammo. Also, the shots rebound very easily and can hurt if they hit you.
Step 1: The Barrel
The first picture shows how you should fix two elastic bands into the connector(sorry for the blurry photo. The rest are much better). Make this part eight times, then build it up into the barrel shown in the second and third picture.
You might need a different number of bands depending on what type you have.