Hi broadaxe,
Sorry for almost overlooking your post.
http://www.vikingsword.com/vb/showth...64&page=6&pp=3
Yes, this is a mid- to second-half 15th century breechloading ship gun, originally mounted on the ship's rail, with its swivel stuck in the wood.
It is preserved completely, including its detachable breech.
After a bit of photoshopping, I reattached your picture.
Best,
Michael