Fascinating. The one on the left with thick walls looks like it could be used with some degree of safety, assuming fairly weak powder. The thin-walled one looks like a demo piece for the original meaning of "hoist by one's own petard"!
All muzzle-loading cannons are supposed to be swabbed out between rounds with a wet sponge to extinguish sparks, which is undoubtedly a good idea with these.