i can send you plans on a suped-up potato launcher.
rifled thick steel barrel for accuracy. a piston drives the payload out of the barrel, not the actual fire. actually coke cans filled with cement are excellent dumb ammunition, but if you want an explosion...
mix black powder, salt peter, and some percussion caps into a baggy and tightly wrap it in a sphere with about 1/4 inch of electrical tape. the whole works should be a good size to fit into the can that is your barrel width. you can then pack the ball into the can with shrapnel of your choice, i like small thin nails. seal the top. these actually make excellent mines. now, extremely important: you need to use a propellant that ignites slowly enough to avoid concussion to set off the caps but powerful enough to get you some good range. 3/4 turpentine and 1/4 parafin is about ideal. GET AWAY from the thing and use model rocket ignitors to set off the fuel.
alternately, if you boil down battery acid (use a glass pot out of doors) until whispy white fumes eminate from it and mix it in equal parts with gasoline, you have explosive liquid that then sticks and burns.
check for vintage army manuals at a army surplus store that will give you some wonderful little recipes. "Improvised Munitions," "Boobytraps," and "Incindiaries" are my favorites, good bathroom reads.
of course excersise the maximum possible caution when destroying things, only do it on private property outside of city limits, and dont kill anyone.
oh, and i am not using these things to fight any kind of war, i am just the crazy person in this neighborhood and i like to see things explode.
EDIT: or join the army.
[ June 03, 2002: Message edited by: sporkme ]