If your debating on buying a 3" vs a 3.5" magizine i would recomment getting the 3.5". Then if you still want to shoot the 3" sheels you can but if you want to go after geese or something late season you will have the option of the 3.5". I have an 870 supermag and i only use 3.5" shells near the end of the season or for geese. I have no problem dropping birds with the 3" shells so if your only goin after ducks it's a matter of preference.