On my Single stage press, I leave the sizing die loose to allow it to float. It still bottoms out against the shell plate. Lee dies have employed the o-ring for as long as I can remember.
My entire Dillon tool head floats on its own due to its design.
After considering many of the ideas put forth, I concluded that my Dillon in its original design configuration is probably more accurate than previously believed for rifle loading.
I would have to use a runout gage to confirm results.
I do hand weigh my rifle charges for accuracy groups.
If you let off on the press handle just as the case starts to get a little snug in the die, it will pretty much center itself any way as long as you shell holder is clean.