This redstone contraption is used like a cannon. This is a great device if you want to troll your friends or desolate your opponents structures and builds.
Step 1: Spacing
You need to make sure you have a 9 block spacing to make your frame of the cannon.
Step 2: Blocks
You can use what ever block that you desire to use.
Step 3: Frame
Make another 9 block row with a 1 block spacing, make sure they are parallel.
Step 4: Round Holder
Place a slab block at the end of the frame to close the frame up.
Step 5: Safety
Add a bucket of water at the very first block from the start of the frame.
Step 6: The Ignition
Now put a block above the area where you had placed you water. this is used to cover up the water area and to add the button.
Step 7: Gun Powder
Next add TnT to your cannon frame(MAKE SURE THAT YOU DON'T PLACE A TnT ON THE AREA WHERE YOU PLACED YOR WATER BLOCK).
Step 8: Loaded
At this point you cannon should look like this, this is called the loaded status.
Step 9: Redstone
Now add restone dust trailing from the ignition button, leaving a 1 block spacing. Now trail this redstone dust all the way to the end of your gunpowder.
Step 10: The Fuse
Make sure that you don't trail the restone all the way to your round holder. Leave a 1 block spacing between your gunpowder and your round holder.
Step 11: The Fire
Now trail redstone from your ignition button to the ground and keep trailing the redstone for only 1 more block after you have hit the ground. And now from the trail of redstone place down 5 redstone repeaters one after the other.
Step 12: The Connection
Now trail redstone the rest of the way from the redstone repeaters all the way up to the block that is next to the slab that is used for the round holder.
Step 13: The Button
Now add the ignition button on the block that is covering the water block.
Step 14: The Round
Now place a TnT on the slab, this will be your round or your bullet.
Step 15: FIRE!!!
Well do what it says to do!!! FIRE!!!
HAVE FUN TROLLING ENJOY