Been there, done that. My first time found an upside down primer on a FTF, at the range. Next time I reloaded, I noticed right off the primer slide was "sticky", and I cleaned and polished it. Now, before every loading session, I clean and polish the primer slide. If it ever becomes "sticky", I shut it down and clean it up.I run a couple of Dillon 550's. One for rifles and one for handguns. My experience with sidways primers is that when the primer slide gets sticky and 'jumps' when picking up a primer there is a good chance the primer 'jumps' in turn. So when I feel that kind of 'bump/jump' I look carefully before seating the primer. Unfortunately when I am cranking out 200 to 300 per hour I don't always pay attention. When it happends I shut down production and clean the primer bar.