This is my first cannon and its is made in a way that it will work in 1.3 minecraft.
You have to unzip the file and copy it into your saves ( search: %appdata% , then open minecraft, saves and paste it )

How to use:

(It comes loaded so skip 1 & 2)

1: put dynamite in the three blocks that have water current.
2: put dynamite in the hole in the top of the cannon.
3: press the right button wait 6 or 7 seconds and press left one.
4: watch your target go BOOM

Feel free to use this design in any of your worlds and modify it and make it better.

Oh and I need video