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 duck shoot target system. Just get out the right plastic pieces and an elastic band and you'll have your own mock duck shoot target practice system made purely from K'NEX rods and other parts. Now you just need to make a K'NEX handgun or rifle and you're all set to shoot little duckies down.