Without pictures, it is impossible to tell

Here is a bit about Neumann
http://www.littlegun.be/arme%20belge/artisans%20identifies%20m%20o/a%20neumann%20freres%20gb.htm

For Belgian proof marks, date codes and maker trade marks.
http://damascus-barrels.com/bp.html

I have a few old Neumann catalogs, if you post pictures, perhaps we can id the model.

Pete

http://www.damascus-barrels.com/Movie.html