The British standard load for a 20 bore for the 2 1/2" chamber gun; which I suspect yours will be, is for a 13/16th. ounce load. Best sticking to European cartridges of that length which have the C.I.P. stamp on the box. We in the U.K. can get Winchester 20 bore cartridges which are the RANGER brand but loaded in Italy and intended for these 2 1/2" guns. It would be interesting if a Winchester supplier over your way could source these. Lagopus.....