I know my model 12 sixteen gauge had to be chamber sleeved (both barrels since it is a two barrel set), and I think the ejector port extended to accommodate 2 and 3/4" shells. My Grandfather's Browning A-5 sixteen ga only had the ejection port extended. If I have any short 20's they all must shoot 2 3/4" shells just fine because I have not done anything to them...Geo