Your press is springing.
when the ram is at the top of its stroke when you are sizing
see if you can fit a .004 or .005 feeler gage or shim between the shellholder and die when it is under full load
OK I will try that. What is the conclusion if I can/can't?
And also just to sum things up, is it the general consensus that the way I'm setting up my die, that I'm doing it correctly? (That is to say, bringing the ram all the way up, then screwing the sizing die down til it touches the shell holder. Then back the ram down and screw the die in 1/4 turn more.)
I'm not without believing that this could be an error in something I'm doing...I just can't figure out what it could be.
Is it possible it's not bumping the shoulder back at all for some reason?