K'NEX is the world's most famous constructive toy, which means you can build just about anything. You can take the K'NEX plastic pieces and build all kinds of contraptions, everything from boats to airplanes to robots to weapons.
Watch this two-part video tutorial to see how to build a K'NEX semi-automatic gun. Just get out the right plastic pieces and an elastic band and you'll have your own mock semi-automatic gun made purely from K'NEX rods and other parts. This handgun is not only fun to build, but fun to shoot.