TNT doesn't seem to launch other TNT. When I made a TNT cannon, the TNT in the water meant to push the TNT meant as ammunition sank into the ground and didn't launch the TNT meant for ammunition. When I tried to recreate this, it happened every time. I don't know if this is intentional but it prevents me from making TNT cannons. I also tried to put 2 pieces of TNT next to each other, and primed one and the other before the first one exploded, and the first one either didn't move the second one at all or destroyed the second one. This is kind of hard to explain, but basically TNT doesn't affect other TNT when it's supposed to, or just destroys other pieces of TNT instead.