If you put the large, tipless cone at the bottom, and then put 2x2 cylinders all the way to the top, It would look slightly better.
A second thing is that, to me, the cannon in the reference pic looks, in lego world, about 2x2. They're just a bit too short, and make the legs closer then they should be. A couple things I don't like however, is the length of the forelegs. LEGO Digital Designer and other digital tools
