there is a way to set the priming detent so that the primers are absolutely centered when being fed into the primer pocket. This "setting" has to be perfect for reliable feeding.
On the left side of the press just above the mounting base there is a black metal piece that is tapered to a point at one end, this "taper is what engages the advancement cog that turns the shell plate. This metal piece has slotted holes in it for a small bit of adjustment. If it is set too much one way, it will advance the shell plate past the primer inserting rod, if too much the other way it wont advance enough. You have to remove the tool holder from the machine to observe what you need to see. With no primers in the machine and looking straight down onto the shell plate ,now observe if the primer seating pin starts to rise when the shell plate opening is centered EXACTLY over the pin. Adjust the shell plate advancement so that it stops absolutely centered over the pin...even 3 or 4 thou. out will result in primer lips being caught periodically on the primer pocket edge causing the flip to happen. The amount of "outness" can be so small that it is almost unsee-able so "trial & error" re-do's will probably keep you frustrated for a bit.