so here is a tutoriul on how to build a TNT cannon
things youll need
6 redstone dust
7 TNT 1 door 1 button 5 glass blocks 7 lader 108 bedrock 2 torches
Step 1: Building the Base
We are using bedrock because it's blast proof, You can also use obsidian in place of bed rock.
place a four by four base
place four more pieces of bedrock then do that six more times
then you will need to come to the back and place six blocks of bedrock then place your seven ladders on the blocks you just placed. They should go from the ground up the middle on the back side.
place 20 blocks, 5 rows of 4. Then on each corner make a pillar 7 blocks high.
then in the middle of the 5 blocks towards the front place a block in the middle and on that block in the middle place a button
and then beside the block that you just placed, place your blocks of glass on top of the one with a button on it and on the right and left place a block of glass and on top of that block place glass
time to place the barrel so place a three by three and do that 6 times without filling it in and then place your 6 red stone dust on top of the barrel, Make sure the red stone dust touches the button block and it goes all the way to the tip.
fill in the roof then build the walls and on the back leave above the top ladder a placed for a door then on the inside place two torches how ever you like
Now for the fun part. Place the TNT blocks inside the barrel. Start at the back of the canon and work your way forward. Stop when you have one TNT block outside the canon. Push the button inside behind the glass to fire and it should shoot!!!! and if you want you can make a target.