I've revised the 'Belgian Maker's and Proof Marks' album to make thing a bit easier, with the essential illustrations much larger
http://www.picturetrail.com/gallery/view?p=999&gid=17575181

From "Trade & Hallmarks on Firearms in Belgium" Bruno Joos De Ter Beerst, 1998







1 millimeters = 0.03937 inches
17.0 = .670"
16.3 = .640"
18.7 = .740"
18.0 = .710"
Choke markings may be found after 1924.

1 kilogram = 2.20462262 pounds
1.3555 Kg = 3 pounds
May also be found on barrels after 1924.

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