Minecraft wiki entry for TNT_cannons, associated text: In order to avoid having to manually place TNT into every dispenser of a cannon, some more modern cannons have been designed to use a minecart or hopper system in order to distribute a large stack of TNT from one location such as a chest into all of a cannon's dispensers. There are issues to using such systems, primarily that nearby minecarts may break if the cannon's charge is too powerful, and the necessary redstone circuitry and hopper designs may be deemed too large or complex to be practical.