I see nobody has answered you yet. I have the O/U, but I'm sure it's the same. Selecting a barrel only decides which one shoots first. You select which one you want to shoot first and then you can go bang, bang. Normally while bird hunting, you would shoot the more open choked barrel first. Not knowing if you have choke tubes or fixed chokes, cannot try to help you as to which barrel you want to select. Bird hunting or shooting at them little clay things?