I thought of giving my opinion on this. One choke that I have that works wonders when I use it is the X-factor Ulti-Full choke tube. It has great reviews online, and I give it 5 stars. I believe when I used my caliper to measure constriction, it read .695 constriction. I also use another choke tube I bought years ago that doesn't have any writing on it. I don't know the brand or the maker, but I do know that it is really tight. On paper at forty yards the turkey is DEAD. The constriction is .669 (17mm).