Pretty sure I don't agree much with anything Randy Wakeman says and I will go with choke dimensions of the chart in Keith's book as they were supplied by The old Ithaca gun company. Both my 37R and early 870 16's are older guns their is no evidence that either gun had choke work done to them. Unless of course someone spent hrs polishing the choke to match the degree of finish in the rest of the barrel. I shoot flying game and targets with all my 16's. Browning made in Belgium are choked dang tight for using modern plastic wads. My sweet 16 with invectors (jap) and citori both have invectors of more open constriction for what they are marked. You can call chokes anything but it's the performance a guy wants. I have been told the extended tubes for my Citori are made by Briley the full measures .628". I would only use that Browning choke chart you posted on evaluating newer guns with choke tubes. Just my line of thought. Mb
