I can't find a mystery here
Mortensen's line of reasoning escapes me. It's a bronze breachblock piece. Not a muzzle loader. It obviously was the subject of a catastrophic encounter. I wouldn't want to have been in the vicinity. Regardless of whether it was on a land carriage or a sea carriage, the bed would have been wood and useless after the explosion ripped this piece apart. With the muzzle peeled open, the breachblock went aft; snapping the grip on something it hit. I myself, never position myself aft of the Lion's Paw.
Many moons ago, Dan pointed out and illustrated how copper sheets were utilized as currency in Sweden. With copper/bronze having value, perhaps this scrap was being transported back to port
It doesn't have to have been a naval gun; only scrap and very nice scrap it is.
About 50 or so years ago, I read an illustrated book titled, "The Motel of Mysteries". Whereas we now ponder ships hundreds of years old and digs that are thousands of years old; in thousands of years, a motel will be excavated and people will be expounding upon the supposed purpose of a water bed, TV, condoms and deciphering the mystery books language, that was found in a bedside draw.