I shoot Pyrodex RS these days, no hazmat fees and you can buy it at most WalMarts and Bass-Pro Shops. For a good discussion on Black Powder and it's substitutes see...
http://www.chuckhawks.com/difference_black_powders.htmIf your powder chamber is deep enough you can use the same load I use for my golf-ball cannon. My chamber is 1.73" and I've found that with Pyrodex the minimum charge is one level tablespoon for a reliable BOOM. I go for a heaping tablespoon.... because Pyrodex is lighter by volume than black powder, the load is about equivalent to 1 oz. black powder. This way you can get about 15 blank shots out of a 1 lb. can of Pyrodex or black powder. The trick is to use a "flour burrito" topping the powder charge to get enough pressure for a BOOM instead or a poof.
Make sure you replace your wife's baking flour or you won't get any biscuits or gravy.
My standard load for a golf ball cannon is 1 to 2 tablespoons of "Pyrodex RS" or black powder, wrapped in aluminum foil, tamped into the barrel with a wooden dowel. Next: 3 to 6 tablespoons of all purpose flour (3/1 ratio to powder) wrapped in foil like a burrito tamped into the barrel tight. This load is LOUD and can be fired as a blank or topped off with a golf ball. The flour burns and adds smoke and the foil is destroyed. Good Clean Fun!
I just ordered another 'golf ball' barrel from Missouri Cannon Works yesterday..... John is good people.
----- UPDATE 12/18/07 -----
I still have not received anything from
John at Missouri Cannon Works..... only broken promises.
WARNING !! John is NOT good people.