Hi Fernando,
I had noticed the metal 'liner' within the bore of the cannon ...but it appears (to me) to be 'flanged' at the muzzle end (ie the metal liner originally extended beyond the wooden muzzel and then was hammered / worked so as to fold back and flattened against the wood of the barrel.
It would not be unreasonable to believe that the cannon may not have been used to fire a projectile ...but to fire an 'empty' charge ...to give the impression that it was fully functional. The use of 'decoys' during battles is a very old tactic. If indeed it did fire projectiles, they must have been relatively 'light' (perhaps grape shot).....this would require less gunpowder...and would exert less stress to the wooden barrel.
Leather cannons ?!!? you must post those pictures...
Kind Regards David
Cross posted and just seen the recent updates .....thanks Rick, so leather cannons do exist ...and I thought Fernando had been on the 'vinho' ...
