Hi Fernando, my friend,
You really deserve being congratulated on this fine, rare and early piece which can doubtlessly be dated as early as ca. 1400!
I attach photos of two handgonnes from my collection which you certainly remember. The smaller of them, ca. 1380-1400, retains one of its originally two iron bands to fix it on the (missing) stock. Just like on your piece, the octagonal barrel shows a broad flat next to a narrower one alternatingly - a very early feature, together with the touch hole being situated quite a bit forward of the rear end. On my piece, the touch hole is 4 cm from the rear, which is about the same relation as my barrel is only 13.8 cm long.
The touch hole of the larger barrel, made in ca. 1460-80, is 6.3 cm from the rear end and has a bulged pan like area around it.
As the touch hole on your beautiful barrel is surrounded by a finely polished and well centered pan moulding which is not by far as heavily corroded as the surroundings, and which is too early for the time your barrel was made, I think that it is a working time amendment of ca. 1450-60 when such pan mouldings first arise.
Well done, my friend! I think your path to early hand cannon has led you far back to their origins already!
Best,
Michael - mad with sheer envy
P.S. May I add that your lovely cat Adriano adds an overwhelmingly natural charm to the old barrel!