Not stupid at all as I found out 6 years ago when my first wife died. I was left with 3 boxes of cremains to take care of. My wife's, my mother-in-law and my mother-in-law's companion.
Fortunately, each had left instructions and I was able to meet all 3 of their wishes. The questions then, what about me. My attorney told me to write into my will. He also told me it really wasn't that unusual. He said a favorite of bird hunters was to load shot shells with ashes to be used by friends on their next hunt.
There is nothing stupid about planning. I think my friends and family would think shooting my ashes out of my cannon would be fitting celebration of my life.
For an over powder wad I will just use a single layer cardboard, like cereal box card board. Do the bowling ball Mortar it will be just 8 1/2" diameter.
It takes a good size cannon to do this. Think about the volume of standard cereal box.
This is the chemistry: "Fire Retardant – This is one of the more surprising uses for baking soda. Believe it or not, baking soda can quite effectively put oil and electrical fires due to its release of carbon dioxide when it comes in contact with the fire." from:http://agreenliving.net/the-secrets-of-baking-soda/
So I wouldn't rely on it saving your house in a forest fire but for a short duration use such as a cannon wad, it should be just the ticket.
“If you're not a liberal at 20, you have no heart; if you're not a conservative at 40, you have no brain.”--Winston Churchill