I believe the 18.0 & 18.2 marks are what the bore diameters were at provisional proof. Apparently the left bore was enlarged by .1mm (.004") to 18.1 prior to definitive proof. The word choke on both barrels should indicate they had at least .2mm (.008") of choke each. I forget the cutoff date now but earlier Belgian guns were marked with both bore & choke diameters, but later ones carried only the bore dia & the word choke if it had at least .2mm of choke. none of the dimensions would indicate a full choke, only the word choke which does not denote the actual amount of choke.
