Minecraft wiki entry for Mechanisms, associated text: To make this design, make a dispenser attached to a redstone clock mechanism and hopper to feed it items. In front of the dispenser, place a powered rail on a block of redstone and fill a chest above the hopper with minecart with TNT. This will rapidly dispense those TNT minecarts onto a powered rail and into a massive crater of their own. It can even tunnel down to bedrock given enough carts.