I have seen a lot of tutorials that teach you how to make a pen gun. Unfortunately I did not have a decent pen on hand to make said weapon. So I used the materials available to make my very own pocket sized BB gun. This miniature weapon is very powerful for it's size, and is very easy to make.
Step 1: Materials
To build the BB gun you're going to need a pair of scissors, 3 plastic straws (the straws I'm using are 19 and 5/8th inches long and and a half inch in diameter), Scotch tape, tacky glue (or any other strong glue), a pair of plier-style cutters, a paper clip, an Exacto knife, a cork, a diffuser reed (if you can't find one of these just wrap a shish-kebab stick in duct or electrical tape for thickness), a rubber band (I used a #32 rubber band), and a large kitchen knife (optional).
Note: The kitchen knife and the rubber band aren't in the picture
Step 2: Making the Barrel: Part 1
Cut each of the three straws down to the preferred size. I cut my straws down to about 5 inches in length.
Note: If you are using bendy straws make sure to cut of the bendy part.
Step 3: Making the Barrel: Part 2
Cut down two of your straws so that they have a slice running through the top. If your straw has lines on it you can use those to make a straight cut.
Step 4: Making the Barrel: Part 3
Slide your first cut straw onto your uncut straw. When you slide on the the cut straw, there should be a small gap between the two edges, this is normal. Now slide on your second cut straw over the other two straws, only this time the that cut line is on the opposite edge.
Step 5: Making the Barrel: Part 4
Take a piece of tape and wrap it around the edge of your three straw tube. Do the same to the opposite end.
Note: The picture shows where and how the tape should be attached, and then wrapped.
Step 6: Making the Plunger Part 1
Take your diffuser (or tape-wrapped shish-kebab stick) and stick it into the cork so that the cork almost comes to the non-pointed area of the stick. A gentle rotating motion of the stick will help you ease the stick into the cork without breaking it.
Step 7: Making the Plunger: Part 2
Insert your stick into the straw until the cork is pushing against the edge. Mark a point on the opposite end of skewer that is approximately a half inch from the straw. Cut at this point with you clippers.
Note: You might want to sand down the newly cut end of the stick. Tjis will help the gun run more smoothly later on.
Step 8: Making the Plunger: Part 3
Gently remove the stick from the cork by twisting it out ( try not to damage the cork or enlarge the hole that you have made). Squeeze a very small amount of glue into this this hole. Reinsert the skewer and let dry.
Step 9: Making the Locking and Firing Mechanism: Part 1
Thread the rubber band through the paperclip (look at the picture for the rubber band's exact placement).
Step 10: Putting It All Together: Part 1
Slide the most outward par of the paper clip down the barrel (look at the picture for the exact placement).
Step 11: Putting It All Together: Part 2
This part is entirely optional. If you want, you can cut off the end of the cork with your kitchen knife to make it more compact. Just make sure not to cut into the stick.
Step 12: Putting It All Together: Part 3
Use your Exacto knife or kitchen knife to cut a groove into your cork large enough to fit a rubber band. I have found that using the Exacto knife and kitchen knife in conjunction is the easiest way to do this step.
Note: This is a tricky step, if anyone finds a better way to cut a groove. just post a comment.
Step 13: Completion
Take your plunger, and put it back into the barrel. Now take your rubber band and run it through the groove. Congratulations, you're done!
Here is a video of how the locking mechanism works:
To fire your weapon, pullback the plunger past the paper clip. Rest the front of the punger on the paper clip's inside point, and load your BB or airsoft pellet (I did not have and BBs at the time, so I could not show the gun shooting anything). Pull the plunger out of the way of the paper clip's point and let go! Be careful about who or what you shoot this at, you can cause serious injury if you hit someone in the eye.