Actually, the 550B automatic primer mechanism does nothing (as it is supposed to) if there is no case at Station 1. The primer in the slide just goes back and forth. It doesn't pick up a new primer until the slide is empty. The powder measure doesn't throw a charge into an empty station, either. So, you can use the 550B as a single stage press if you want.
As an alternative to using the 550B as a single stage, which involves loading trays to hold the "batch" in between steps, you might consider using it as kind of a twisted turret press.
Insert a case at Station 1, size / deprime / reprime.
Index to Station 2 and do the bell and powder charge.
Index to Station 3 and do the bullet seating to your desired depth.
Index to Station 4 and apply the crimp.
Index to the collection bin and check your finished round.
This probably resembles a turret press more than anything else, as only one operation is happening per handle pull. If you feel like adjusting something at a station, you aren't interrupting progressive operation. (Which is one way double charges and squibs happen...operator adjusting the powder throw at Station 2 during a "run" instead of making adjustments between runs.)
I pause after a run of 50 to box the completed rounds, label the box, check OAL and weigh a sample charge into a case I reserve for this. (It has a fired primer instead of a missing primer... )
That way, if something crazy happens to the press like the linkage for the powder measure partially disassembles itself, I only have to pull down one box.
This has only happened to me once, and I'm not going to join the club where the reloader has loaded 500 rds before he finds a mistake.
