I've recently tried what was previously suggested here some time ago, that is to shoot light 2 3/4" loads in a 2 1/2" chambered gun in good condition. My normal target load is 1 oz. 2 3/4 dram 1180 fps. Estate shells, that measure 2 5/8" after being fired. Last Sunday I tried it out with my usual RST 2 1/2" 1 oz. 1175 fps loads to compare. Other than a slight amount of barely perceived recoil, it worked fine, without any shredding or burning of the case mouths. My Churchill may have "generous" forcing cones, but it worked well.
Good to know with the current supply situation of 2 1/2" shot shells!
Karl