As you can see in this video TNT is not working the way it should i believe what happens is that the TNT almost forgets it is in water and blows up the TNT cannon. But in the video after the TNT cannon blows up i go over to the exact same TNT cannon just built in a different place and it works fine. I have also built this cannon on my phone and it also blows up which it shouldn't because the TNT is in water.