Want to make a cool easy to make TNT cannon? Well this is the one!
You will need items seen in my Hotbar, recreate what Is seen
Add water and 3 more dispensers as well as slabs
Put 4 blocks to keep TNT from blowing up to soon
Add red stone, and fill up dispensers with tnt
Now press button and before TNT blows up, flick lever 4-5 times