Fabrique Nationale of Herstal was an absolute giant in the industry when this shotgun was produced. Yours seems well cared for from what can be seen. I would suggest that you attempt to identify the model. It appears to have some quail / grouse / dove hunting left to do, with the proper loads. Abby at Cornell Publications has a reprint of their 1928 catalog:

http://www.cornellpubs.com/Templates/Browning-FN-1928.htm

I recently got out bid on a 1920 catalog from FN. The final selling price was over $300....ouch!

Pete