I happened to have a set of calipers this weekend and decided to check all of my chokes. I checked a Rem Modified, Rem Full, Rem SuperFull Lead only, Rem SuperFull HS*Steel*Lead, Mad Calls Super Max, and Hybrid. All chokes were for my Rem 870. Here is what I found when I checked them. It is listed as Entrance Diameter, Exit Diameter, Length, Constriction.
Choke Ent Dia Exit Dia Length Constriction
Rem Mod: .742 .709 2.032 .033
Rem Full: .740 .689 2.031 .051
Rem SFPB .741 .665 3.031 .076
Rem SFHTL .735 .670 3.028 .065
Mad SM .742 .672 4.121 .070
Hybrid .744 .669 3.496 .075
The only 2 that checked out at what they were supposed to be were the two Rem SuperFull's. I looked at constriction per inch but since not all chokes gradually constrict, and rather constrict fast then stabilize, I did not include that data.
I understand what you are saying. Unfortunately I could not measure the Barrel Dia. so All I had to go in was the chokes.