I made this gun in a boring class, and it can shot a small paper ball for 5 meters.
-a piece of paper ( I teared it from a notebook )
-a ballpen ( something like the core also works )
Maybe you need something to cut the tape.
Step 1: Split the Paper
Portrait split the paper to 2 parts from the middle.
Step 2: Disassemble the Ballpen
Disassemble the ballpen, take the core out.
Step 3: Make the Striker
Roll a strip of paper with the pen core as tight as you can.
Glue the tip.
Pull the pen core out.
Step 4: Make the Barrel
Roll another strip of paper around the striker.
Do not roll it too tight.
Glue the tip, too.
Make sure they can slide smoothly.
Step 5: Tape the Rubberband On
Pass the tip of the tape through the rubberband, then tape it on the striker.
Tape another tip of the rubberband on the barrel.
Step 6: Have Fun!
Fill a small ammunition in, pull the striker, release to fire.
I am going to make a auto refill one
Sorry for my poor English.