TZ this is one time when I wish I could find a good way to argue with DD. The barrel looks sound, but is of unknown age, and unknown material. Also the history is unknown. Even if the exact alloy could be determined, the history is still not known. There could be micro fractures in the barrel just waiting to rupture, and spit pieces of barrel into any near by persons.
It is a nice looking bit of ingenuity, but I must also recommend it not be fired. Sorry.
Well made and fully servicable cannons are available from the sponsors of this board, and other outlets. Perhaps you could have one that is safe to shoot for next year.