TNT cannon

Short Summary
To make a TNT cannon, you simply just need to make a half barrel shape cocoon using either Cobblestone or Obsidian. Of course, you will need TNT but what some people might forget is that you also need at least 32 redstone dust and 1 switch or button to activate 4 pieces of TNT.

Creating
If this does not help, follow this link:[] It is a video that shows you how to make a TNT cannon.

Step 1:Making the barrel First, make a line of 5 cobblestone blocks with one more block on each side(Preferably third block)you need these to add the side lines, make sure those are again, 5 blocks across. Now add 5 more blocks to one side. To finish off, make a 3 block high line to the back of your cannon barrel and fill in the corners with 1 block.

Step 2:Adding the redstone dust and switch This is going to b a very short step, so we will put it in detail for you: So the TNT does not activate, do NOT place any TNT yet. Place redstone dust on the 2 blocks at the back, and we say 2 not 3 as the switch will need to go on the block next to the higher side. Now for the activation of the TNT, on the 2 sides place redstone dust on the 2 closest blocks to the back. Just add the switch on the back part that does not have the redstone dust on and you are ready to get onto the next step!

Step 3:Water, Half-block and the TNT!!! For the beginning of this step, place 1 half-block or 1 whole block at the part where the TNT will be shot(At the end). Now place water opposite the half-block so the inside 3 spaces are filled up with water. Be warned with this part! If the switch is activated while you arm the TNT, the place you are building in will cause a large explosion!!! Starting with the end, place TNT towards the place where the water starts(Except for the main water point and the half-block.) and place some TNT on top of those two as well.

Now your done! Add TNT on the top of the half-block and then flick the switch, wait a short while(Making sure the TNT does NOT explode!) then activate the TNT on the half-block and RUN AWAY!!!!!!