I finally took the base of my .223 sizing die to the belt sander. Had to take about .005” off. Now I can size correctly without stressing the press. I had to do the same with my trim die also. Apparently, it’s not that uncommon.

I ran into that with a rcbs 06 shell plate for the rock chucker.
Took it to the lathe and trued it up.
I suspect the belt sander was not able to true up the square plane and it is still wop sided.

A lathe would have been ideal. At least I can size the brass level with the bottom step of the case gauge. The best I could do before was level with the top of the case gauge. I don’t understand why anyone would want to stress the press by turning the die down 1/4 turn past making contact with the shell holder. At 14 threads per inch, 1/4 turn is just under 0.018” unless I did the math incorrectly.