Here is a really simple pen gun than is quite powerful and has a range of 20+ feet. I finnaly got around to making this instructable so I hope its alright
Step 1: What You Will Need.
you will need,
1.cheap Bic roundstick pen
3.very small nail
4.lighter, candle or small drill bit(same size as nail) and drill
5.Plastic report clip.(peice of plastic that clips onto papers to hold them together but you can use about anything that can fit in the pen, blocks part of it off and can be cut to size)
6.Retractable Sharpie. (we need the spring from it)
Step 2: Ready the Pen
Remove tip and ink tube.
Step 3: Remove the Ink Tube
Remove the ink tube
Step 4: Sand the Tip.
sand the tip of the pen so it can slide out of the pen tube easily.
Step 5: Savage the Sharpie
Take apart the sharpie and remove the very large spring that fits perfectly in the pen tube.
Step 6: Ready the Spring
put a small piece of tape on the sping so it doesn't fly out when fired.
Step 7: Fire! Fire! Yea! Yea!
use a candle or lighter to heat up the nail.
Step 8: Make a Hole
make a hole through the pen tube and cap with the hot nail. (here is where you can also use a small drill bit.)
Step 9: Make Spacer
cut your material (peice of binder clip, plastic etc.) so it is to size so it leaves room for the tip and fully compressed spring
Step 10: Aim and Fire
to load the gun just put the spring in the pen and jam the tip on the sping and insert the nail to lock it in place. to fire just aim and pull the pin