I've shot a goodly amount of Bismuth shells out of my Super-Fox, in both the 32-inch barrels with .053" and .051" choke and the 28-inch barrels with .012" and .017" choke without any ill effects. All 2 3/4 inch 1 3/8 and 3 inch 1 5/8 ounce loads. I've also shot a good bit of Bismuth out of 16-gauge bird guns in the uplands with good results and no issues.
The only two doubles I've ever had loose rib issues with are open choked bird guns that have never seen a non-toxic shell of any kind.