The 1924 rules mark does not give the diameter of the choked portion any more, just the unchoked bore size.
From littlegun.be:
JANSSEN Fils & Co (Banc dpreuve de Lige 1895 1937) et sise rue Lambert Le bgue, 4 LIEGE.
Etablissements JANSSEN Fils & Co S.A. (Banc dpreuve de Lige 1937 1951 ) sise LIEGE rue St Gilles,87.
Fabrique dArmes JANSSEN Fils & Co S.A. (Banc dpreuve de Lige de 1951 1954) rue St Gilles, 87 LIEGE galement.
Assuming the inspectors' marks add up manufactured 1937...1954 (probably little production during WWII).
Markus
