Unfortunately, even an "over-built" BP cannon + can of Bullseye = bomb.
Most folks know that you shouldn't mix bleach with ammonia, yet many have them right next to eachother on a shelf. Only the knowledge of a bad reaction prevents people from pouring them into the same bucket.
Best we can do is build sturdy and keep our personal cannons, powder, etc. secure, while educating others about the hazards associated with them. Just like a band saw or other power tool; if a cannon wasn't somewhat dangerous it wouldn't be good for anything.