Minecraft wiki entry for TNT_cannons, associated text: This type of cannon is easily constructed, very powerful (practically infinite) yet flexible with its charge and hilarious to watch unfold. The only downsides are that it requires an active ender portal and you will need to be in creative to survive maximum charge. It operates on the principle that the fuse timer on primed TNT is reset to 0 when it passes through an end portal. This means that a potentially infinite amount of TNT can be used as a charge, simply by condensing it into 8 blocks of space. Minecraft will not detonate them until you are in the end, thus making the computer itself the limiting function.