make sure you use a good peice of coper pipe that has been capped and welded shut then for the piston itself... a peice of steel rod that has been annealed in a good hot fire... once cooeld you can start to thin it down to just fit it into the pipe using sand paper and maybe some pumice paste made by pulverising it into powder and mixing it in animal suete or you can use a grainy toothpaste......this will polish the rod and get it into a finer fit ... if you need to you can use an o ring about four millimeters from the base... ... once you are able to set the rod in the pipe and the presure from the air caught inside you can put it into a peice of wood and fit a strike cap for the piston itself... next... yo ucan use a dremel and a dimond grinding bit to shape a small cup in the bottom of your piston.. the best tinder to use is a peice of dry, rotted wood that is spongy soft... if you are still having troubles make sure your fitting is really tight at least right at the last five to ten millimeters of the piston... hope this helps
