Did you forget the water? if tnt goes off in water it doesn't destroy blocks. Or, are you hitting the buttons in the right order? you need to hit the one connected to the water area first, then you have approximately 3 seconds to turn around and hit the other.
way to complicated for a "Basic" cannon
look at mine
9 full repeater is the optimum delay to fire the cannonball
Cool! I agree my cannon is far from basic, but it's basic in comparison to other cannons I make that fire multiple shells and have a charge chamber bigger than my house, lol. I dont usually make auto cannons, so the repeater firing is new to me.
Thanks for the feedback!