This is my first post so i don't know exactly what to do. Here is a video of my marble gun it can shoot semi auto or single shot. i became interested in these because of spudfiles.com now i have a site that sells them it is freewebs.com/pats-spuds so you can check that out too. the gun only cost about $45 to make. in single shot at 70 psi the marble will go through a 3/4inch piece of plywood.the video is shot using semiauto at 35psi because that is as high as my pump will go. hope you like it.