Sorry Mssgn, I can't read all the marks on that picture.

You'll find here a list of identified Belgian (essentially from Liege) gunmakers (on the left column you find the marks they used to identify themselves, on the right column, their complete identification)

http://pagesperso-orange.fr/mallorquina/source/recherchedesmarques.htm

On that site can you also identify gun proof officer who tested the gun and year of production.

With those informations you could find more informations about the guns the gunmaker produced here: http://www.littlegun.be

If you can't find the caliber that way, you can contact "littlegun" by e-mail, I think you can contact them in English (if not, I can help), it's the best resource I know to find informations about old Belgian guns.

If it's OK for you I could post the pictures on the Belgian Gun owners section of a French forum.

Va t'in tch�re !