Minecraft wiki entry for TNT_cannons, associated text: The shot mounting block for a cannon should be chosen according to how fast, far, and high you want the cannon to fire. Of course, these variables depend greatly on the position and amount of the charge and the timing of the shot, but the mounting block also can make a difference. For example, with a cannon with a charge of 5 and a delay of R4.3, the shot will take a mortar trajectory with a ladder more than with a fence post and pressure plate.