[kronckew]

if a keel boat gun, may have been loaded with a charge of musket or pistol balls as a large shotgun for repelling boarders. would bronze corrode in fresh water,
and likely covered in sediment restricting oxygen availability, like that in a couple of hundred years? 2000 yr. old roman bronze artifacts are usually in better shape. if it were galvanic corrosion based on the steel bore insert, i suspect that the iron would have gone before the bronze.

i recall reading here about small indonesian cannon (lantaka) that turned out to be bronze or brass sheet over a concrete core with a iron or brass pipe bore. caveat emptor.