Welcome to a cannoneer’s paradise, Millsman. The answer to your question is easy; anything that relatively seals the bore and provides some resistance to the pressure of the ignited charge moving it out the barrel is going to make any piece of black powder artillery make a bigger bang, although a mortar isn’t going to be as loud as a cannon. Now for three things that aren’t so easy: You can’t use something as a wad that’s going to bind too much in the bore because this could lead to dangerous pressure levels, you have to be aware of the dangers of starting a fire if your wad material is going to burn, and you have to be aware of the dangers of injury or damage to property if your wad material will act like a heavy projectile in its own right (like wet newspaper). Other than some silly things used in my youth, the only wads I’ve used have been cork, dried compacted grass, and thick felt wads. Another member was recently talking about using an equal amount of flour on top of the charge. This sounds interesting, as it would seal the bore, provide some weight to offer resistance, and it wouldn’t pose a danger as a projectile; I think I’ll give it a shot the next time I go to the range.
