The failsafe solution I've come up with to avoid primers winding up upside down in the tube and subsequently in my casing that way is simply watching them as they drop. If I get one that flips, I stop the machine, dump out 2 or 3 and then continue.
Re adjustments, the biggest thing I've done that helps is beveling the edge of the plastic colored insert where the primer drops. If it isn't lined up perfectly, the square edge bumps the primer on the way in and kicks it up onto it's side. By squishing the edges of the plastic slightly where the primers enter, it seems to remedy some of the problem. Still not 100%, but aside from adjusting the rheostat correctly, it's the thing that seems to have helped the most.
I've also noticed that if the line of primers gets too long (like when all the primers start already in the hopper) and they're pushing too hard on the one that's dropping, the incidence of flipping seems higher. Along those lines, when I dump a new card of primers, I let them drop from the clear plastic housing into the hopper slowly via the machine's vibration instead of pushing them all in at once, if that makes sense. It seems to help a little. I also adjust the clear plastic "stabilizer plate" a touch more snugly than recommended and find this does the same thing; holds up the line a little and takes some pressure of the primer that is currently dropping.
As a disclaimer, I've only owned my RF-100 for 6 months or so. These are just some uneducated tweaks that seem to help. And while the machine is fiddley and a bit of a pain in the ass sometimes, it beats the tar out of bending over and picking primers up via the tube, one by one, IMO. I LOVE the thing and despite everything consider it one of my best reloading investments. [shrug]
Also, check this guy's video out. I've not tried his solution yet, but he seems to think it makes a big difference…
https://www.youtube.com/watch?v=fEXB40qgMV0
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