My model cannon. Cannon is a bit over 13"long, 2" OD at widest, .75 bore.
Oak carriage with 6" wheels, and used slices of 6" pipe for rims.

I keep looking for the right piece to make one that fires the small juice cans full of concrete. The full meal deal that fired a 48" can might make some of the people I make nervous a bit to nervous. LOL