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.