My family has been hunting with over and under shotguns since the 60's. We shot the more open barrel first, shooting over decoys, duck hunting and then had the full choke as the birds would get further away. Turkey hunting would be the opposite. Shoot full choke inside 30yds (turkey standing still) and if the turkey ran or flew after a miss you would have the modified. My dad always taught me to make the first shot count and don't plan on a second shot. If you are shooting 40yds you might as well have the same choke in both barrels. One shot situation. Even these days the majority of turkey's I harvest are inside 30yds. I set up my gun for the scenarios I encounter the most. My kids hunt with a 20 guage over and under with a Pure Gold .570 on top and a factory full choke on the bottom. One shot is what we are looking for in the turkey woods. Let the turkey get close and if there is a miss he has the more open full choke for the follow up. As they continue to hunt and get more skilled I will put a PG .555 on the top and move the PG .570 to the bottom. Just one way to set up a gun, not the only way.