There is a piece on the web, somewhere, about a working model, don't recall where just now, but I believe the site sells carbide cannons.
Many years ago I bought a set of plans to make a working model of a Whitworth cannon, carriage and all, chambered in .45 Long Colt. I looked a few months back and the plans were not where they were supposed to be. There is a lot of stuff in that room, so it's going to be awhile before I track them down, if I can.