Chades powder equals...

[maulkin]

I agree canon would be fairly useless against dragons. Dragons are way too manouverable!

It seems to me that cannon could be quite effective against dragons if used defensively (e.g. in batteries mounted on castle walls) and a charge of grapeshot or chainshot could make a real mess of a dragon's wings. A liveship mounted with cannon would also be truly frightening, the figurehead could even hold and aim one!