I made this last year in 6th grade. I got the idea from my friends and then modified it. I had one of the best guns.
1. the materials
2. dissasembling the pencil
3. inserting the spring
4. reassembling the gun
6. shooting (I really think that it is self explained)
Step 1: Materials
1. at least 1 paper mate .7 size mechanical pencil
2. a pen with a good spring
3. bic .9 size erasers usually comes with lead refills
4.a pencil grip (optional)
Step 2: Disassembling the Pencil
this is simple:
Unscrew the tip. Doing this will also loosen the rest take this off. if there is any more lead take it out. the inside is made of three parts: the darker part with eraser on it, the part that holds the lead, and the other end that screws into the black tip---pull this off it may take a while but it will work.
Step 3: Inserting the Spring
finding a spring is the most important part. i test my spring by pressing the pen button down on the counter and then letting pop up. the one that jumps the highest wins. take the spring out and insert it in the clear part of the one end i had you remove in the last step. if it doesn't fit find a new one make sure that it's tight and won't fly out when you shoot.
Step 4: Reassembling
take the spring part you made in the last step and glue or tape it to the part that holds the lead.then place it back into the shaft or whatever you call it. make sure it slide around pretty smoothly or it may not fly as well.
Step 5: Bullets
i use the bic erasers for this step. you can customize them for different situations. i colored one red so you could see it on a white floor. other erasers could work though.
Step 6: Shooting
take the eraser and insert into the end where the tip used to be. just press on the eraser end and watch it fly. mine isn't the most accurate so i took a pencil grip and put it over the end so it would go straighter.
but try whatever if you keep working you could probably come up with something better.