Disclaimer: USE THIS AT YOUR OWN RISK. IT INVOLVES EXPLOSIVES AND IS PROBOBLY NOT LEGAL IN THE USA. I AM NOT RESPONSIBLE FOR ANY DAMAGE THIS CAUSES.
to start, you need these things:
-3/8" galvanized steel pipe 6 to 12 inches long with threads on the outside of the tips
-firecrackers, flash powder, or black powder (gunpowder)
-1/4" steel slingshot balls
-paper towel or napkin
Step 1: Fixing the Barrel
Step 2: Drilling the Endcap
Step 3: Obtaining and Using Powder
in terms of quantity, you should never use more than about half a teaspoon of any powder. i have never tried any more, but if you think my rig is strong enough, use your best judgement, but remember: I AM NOT RESPONSIBLE FOR ANY DAMAGE. start out with a tiny amount and work your way up. if you load in way too much, the pipe will explode sending hot metal shrapnel in every direction, all before the ball even leaves the barrel. as for black powder, i have no experience with it. therefor i have no idea how much to use. as i said for flash powder, use a tiny amount the first time, and work your way up.
if you only have firecrackers, you have to spare a few. you can either put it directly into the chamber (be careful because the fuse to most firecrackers are very fast). to get a pack of firecrackers apart, untangle the threads or strips of paper that hold them together. take a razorblade and slice one of the firecrackers in half at the middle. hold the pieces above a sheet of paper and squeeze it while rolling it between your thumb and index finder. the dark grey stuff is flash powder. if you see reddish or light greyish stuff, that is not flash powder. don't let too much of it get into your flash powder. when you have enough powder, fold the paper in half and put it aside.
Step 4: Loading the Cannon
take your cannon and insert the fuse about a half inch in the hole you made. tape it in place. grab your paper with the powder on it and slowly pour the powder into the top of the barrel. when you finish, put the slingshot ball in the top of the barrel. make sure it goes all the way down with the ramrod. then, rip off roughly 1"x1" inches of paper towel and fold it twice in half to make a 1/2"x1/2" square. jam that down the barrel with the ramrod until it hits the ball. now you can tilt the cannon down and the powder won't fall out. :)
Step 5: Firing
WARNING: DO NOT HOLD IN HAND WHILE FIRING!
put the cannon on the ground. you can put a rock or something under the front of the barrel so it tilts the cannon up so you can actually shoot at stuff. put something behind the cannon because it can fly back. make shure there isn't a pile of leaves behind it, otherwise you could lose it. remember: for every action, there is an equal and opposite reaction. when you are ready, light the fuse and run away. think were it will ricochet, and don't go there. depending on the amount of powder you used, it is very loud (similar to a gunshot) and very powerful. i suggest to get out of the area you just shot at in case someone called the cops. i've shot through an old license plate and peice of a 2 by 4, so watch out, it has the potential to kill.
PLEASE use every precation you can think of. i don't want to get anyone hurt. if i do, i am not responsible.