Scott,

It would help if you posted pictures. The gun is Belgian. Here are the proof marks and maker's marks:
http://damascus-barrels.com/bp.html

Janssen was a family of gun makers. Here is a bit about them:
http://www.littlegun.be/arme%20belge/artisans%20identifies%20i%20j%20k/a%20janssen%20freres%20gb.htm

Pete