Minecraft wiki entry for TNT_cannons, associated text: The Bad: Unfortunately, cannons of this variety are bulky and often unattractive. They require sand or gravel which are nonrenewable resources in survival mode. Added to that, it is tedious to reload the cannons whenever the magazines run out of ammo, however occasional that may be. With standard TNT cannons, if the 1-round magazine is destroyed, it is usually easily replaceable. This is not the case with the reloading kind, as the entire magazine will explode, destroying the weapon and all the redstone wiring with it—often killing you in the process. This type of cannon has also become redundant with the recent updates allowing automatic cannons utilizing dispensers to reload the tnt, which is easier and more compact to make.