The gun was made 1910-1921 (there is no lettre annale)
It does not carry smokeless proof, which was not mandatory until 1924. That is why there is no chamber length over diameter mark.
It originally had a bore of 18.3 = .720" with a L muzzle constriction of 17.6 mm = .693"
Not sure why the R doesn't carry the 18.3 but if the muzzle constriction was < .008 it would not be marked CHOKE.
It was reproved after honing to 18.5 mm = .728 and the L choke is now .697" and R .717"
Belgian guns for export commonly did not carry smokeless proof, but the barrels are quality Siemens-Martin.
The Belgian pre-1924 Max. 12g load was 1 1/4 oz. 3 1/4 Dr.Eq (1220 fps) and period loads ran about 10,000 - 10,500 psi with Dense Smokeless.
I'd stick with 1 1/8 oz. at 1200 fps if the barrel wall thickness is adequate and head of the stock is without cracks.
