This started as an intrusive thought but now I need answers
Soda cans and tennis balls fit a 2.5" barrel (hard to find 2.5" PVC). Not sure about bottles.
for this application no rag, classic style with storm matches taped to the sides. should be windproof enough to stay lit
good point. maybe if they were along the neck of the bottle and it was loaded bottom down
I'd suppose if you wrapped the bottle in a T-shirt, it could fill the space well enough. It might or might not decrease the likelihood of the bottle successfully shattering though.
If you're interested in firing some kind of improvised munition from a cannon, might I recommend soup (for your family)?
It'd probably work. Che and Fidel used to teach their guys to shoot molotovs by putting a wooden down in the throat of the bottle, fitting that in to a 12ga shotgun, and then firing it to create an improvised mortar round. Apparently they did work.