A TNT cannon that fires TNT for a very long time without refilling.

TNT cannons -well and good, but the annoying reloading after each shot is very annoying and spoils the fun of blowing holes. Here is a variant where you only have to press the button and then just wait.

Instructions:

First you build the simple TNT gun from seven TNT in a row and water in front of it. On the opposite side, one block higher another TNT and wire the whole thing like on the screenshot (far right). The magazine itself consists of pistons with gravel on top, there must be as many gravel blocks as TNT blocks, so that all TNT are shot to the end. The pistons under the gravel are connected by redstone flares, the redstone track leading there needs more delay than the TNT that is shot away at the gun, so that it is reloaded only after it has been shot. To make the whole thing automatic, I took the redstone track with the biggest delay (the one towards the magazine) and connected it to the beginning, creating a clock with a lot of delay. The magazine can be built as long as you like. P.S.: I put water next to the TNT in the magazine, so that nothing flies into the air.