In order to double charge a case in a 550 you would have to try to put a bullet in a case that already has a bullet in it, try to put a new case in the first station that still has a case in it and ignore these and not turn the shellplate. I have had my 550b for about 25 years and haven't done this yet. Turning the shellplate with your left hand as it moves to grab another bullet becomes automatic after pulling the ram lever. While doing this your right hand grabs and installs another case. Going slowly at first, maybe 200 rds per hr, and it soon becomes automatic. I still do not reload while distracted by anything even a radio. I'm not saying the 550b is the best press for everyone but it's the best I have used for me. The only thing it has ever done wrong is to not feed a primer maybe once or twice per thousand. Not dangerous but makes the need for occasionally pulling a bullet.