Nice thing about Belgium guns I have dealt with they have the bore and choke size marked on the barrels, if they are nitro proofed and still within couple thousands of that I feel pretty darn good about them. My Belgium double 16s are all marked .669-.670 but in mm. Now Fn brownings are all over the place on original bore size. This one was original 70mm chamber it’s probably beefy. Hope nobody got out the brake hones.