I found this idea over at Sugar Bee Crafts and knew it would be a hit with my two. You can find the exact measurements on their site. Just click on the link above. It cost a little over a dollar to make. We just went to the hardware store for the PVC. We laid out the pieces and the kids put their shooters together themselves. T loved this part, but he is a puzzle lover. In the past few days he has taken it apart and put it together so many times. We tried shooting marshmallows but the kids kept eating them so we switched to shmuzzies (pom-poms). We have been having so much fun. Go on over and check out Sugar Bee Crafts, so much great, fun stuff over there.
(Sorry for the fuzzy pictures, my camera was acting up)