You're not using enough wadding or not tamping it down tight enough. You only need 20 grains of black powder and a good tight wad, and the cannon should crack like a pistol shot. Or at least the boom of an early pistol. I have several of the same cannons on original carriages and they make a great sound when shot. Try tamping the wad down with a longer rod like a dowel, use paper that packs down tightly. The barrel is brass so it won't blow up if used properly. The barrel by the way is from around 1900 give or take 10 years or so. I also have found small ball bearings that fit and shoot them, but you need to do it in a proper safe setting because they will fly out like a pistol bullet.