Hello
I'm grateful for your your comments. Trying to clarify some points that were raised, I searched all the gun’s surface with a magnifying glass and I found a small word (letters of 1 mm size) engraved in half-circle: Casteres . Tried to google this word and found it is a French name, in some cases from aristocratic families. I’ve uploaded a photo showing where this word was engraved.
http://inscription.notlong.com(Doug: the Fotki website seems to show the photos for as long as one wants, unless the slideshow mode is activated).
I don't know if this relevant as I wasn’t able to correlate this name "Casteres" to anything related to guns and I didn’t found any other words or marks, or evidence of an erased mark – but this is a real possibility, I’m no expert.
Concerning the history of this gun: my grandfather was an obsessive hunter and shooter. He owned several very good shotguns (in different occasions he had one Holland & Holland and one Greener). He bought and sold these guns frequently and he knew a lot about them. Since my childhood (I’m 56) I remember that he kept this gun with a very special care, and he never let me use it. He always said I would inherit it, and so it happened (my brothers kept other guns). He never disclosed the brand of the gun, I don’t know why – he called it the “hammer shotgun”. He lived in Portugal, where the gun is now, and I think he owned this gun at least since 1950.
Thanks again for your valuable advice
Joao
