When I load with a single stage press I charge all cases whether 10 or 50 and then I look in all cases to make sure there is powder in them and no double charges, then place the bullets in the cases. Make sure you have good light and LOOK in each case. If you choose to do one at a time, LOOK in the case before putting a bullet in it. It's easy to fail to charge one doing them one at a time, very easy.