Step 1: Lets GO!
Ok, now we need a click pen. The one pictured works best (and they are mostly free from car delerships) because it comes apart nicely.
We also need a lighter, or like i did the first time you can use a stove if you are really carefull. A projectile can be found later, i use erasers from cheap pencils.
DISCLAIMER: this project can possibly injure somebody. I am not responsible for any injuries, damages or deaths related to the fabrication or usage of this product. Allways use common saftey sense and proper saftey equipment while fabricating or using this product. It can shoot over 100ft and still sting a little.
This was origionally posted my me at (http://sirscamit.tripod.com/id12.html)
Step 2: Pen to Barrel
Now take the plastic straw from the air duster and stick it into where the ink tube was not so long ago. It probably wont fit too snugly so this is where the lighter (or stovetop) comes in. CAREFULLY melt the tip untill it's barely soft and roll it on the desktop to shrink the diamater of the tip to fit the straw fairly snugly.
It should be fairly difficult to pull it off of the straw because it will be holding pressure later. Now we need to finish up. If my vague discriptions haven't helped, the pictures should help.
Step 3: Looking Sweet Yet?
After years [and by years i men about 2 min] of R&D; I discovered that your average eraser from an el cheapo [or free] wooden pencil works very well. If its too small, try a different eraser, there are 2 normal sizes and the biggest one works the best.
I have found that using some oil [i use reel oil, but 3 in 1 oil or similar will work] helps out a lot with getting a snug but not too snug fit with the eraser. If the eraser fits too snugly, the whole barrel will go flying, which is pretty cool, but not as fast. If you shove the eraser down too far, you can use the straw to push it back out to a good firing fit.
In my tests, my basement is a little over 100ft long and it goes all the way to the other side without too much arc. Be carefull when shooting, it can sting, and possibly maim, so use common sense and if you lack this, do not make my project. ENJOY!