Simon,
Before going into the required details, I would have to see the following close-ups:
- the muzzle slightly slanted, and the present caliber measured in mm
- the area where the original rear sight was fixed to the top base of the barrel
- Are there traces of a former foresight - I strongly expect them to be there!
Based on this information, I could tell you a lot more, especially as the originally dove-tailed pan and cover were obviously removed as well, so the barrel itself is just a fragment compared to what is was like almost 500 years ago, and I am afraid it will never look the same again. Anything you might probably add, in my opinion, would not by far come in the slightest near the original impression.
Best,
Michael