Here are the Belgian proof marks:
http://damascus-barrels.com/Belgian_All_Proofmarks.html

Miller is correct. It was proofed between 1898-1923. It was nitro proofed. At time of proof, the barrrels weighed 1.261 kgs or 2.78 lbs.

As Laurie stated, it is a Francotte. For more about Francotte:
http://www.littlegun.be/arme%20belge/artisans%20identifies%20francotte/a%20francotte%20gb.htm

To help id the model, go here:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=229328#Post229328

Pete