I have a bronze cannon with a 1.5 inch bore and 34 inch tube. The breech is almost 5 inches thick. Last time I fired it, I loaded 250 grains of 1f cannon powder and 3 - half inch thick homosote wads. The bang shattered windows a third of a mile away. Why in the world would you load almost 900 grains just to make noise??
Back in about 2002 at a 4th of July picnic, near Gettysburg, PA a fellow was shooting a home made cannon, just for noise. After about 12 shots, the thing blew up killing a bystander that was 25 ft away. The fellow is getting out of jail in a couple months. Charged him with Negligent Homicide.
Cannon accidents are bad enough, accidental cannon injuries and fatalities lead to the illustrious leaders thinking the average joe isn't smart enough to be trusted with a spit ball. Be careful. Be over cautious. Don't give the anti's any reason to take away the fun from responsible folk.