When my Brother was 12 he made a small cannon out of copper pipe and a 2X4. He used match heads as powder and just heated it with matches until it fired.
To my amazement, it worked. Too much trouble to fire very much tho.
yeah. When I was that age we made a mortar. We made our own gunpowder from saltpeter(potassium nitrate) and flowers of sulfur we bought at the drug store. The carbon was crushed coal from my basement. Somewhere I learned the formula for gun powder and we had to try it. Eventually you couldn’t buy either saltpeter or suffer at the drug store anymore. This was in inner city Chicago by the way.