This is a simple pen gun I made in the spare time of my math class with only a few common materials.
Step 1: Materials
1. Capped Bic. Pen
2. Any spring from mechanical pen
3. Dull or unused pencil
4. Pencil eraser
Step 2: Remove Top of Pen Cap
This is in my opinion the hardest step, remove the top of the cap of the pen by pushing the pencil through the top of cap.
Step 3: Remove the Pen From Body
Pull out tube of pen after taking off the cap. It might take some grip.
Step 4: Put Spring on Pen
Slide on the spring onto the pen and gently place the pen 3/4 of the way inside the tube. (DO NOT PUT THE PEN FULLY INSIDE)
Step 5: Cap the Pen and Place Eraser on Top
As shown you first put the cap on which should slide through the pen. Then put the eraser on top to keep the pen from flying out.
Step 6: Enjoy!
Enjoy this cool pen by surprising your friends with a shot at them. (To shoot you flip the eraser off of the cap.)