Posted this on several other threads, but it comes up from time to time.
I had a similar problem, where I could not get any shoulder bump at all-measured, with the LNL headspace gauge.
It was suggested I send the die back to Hornady for grinding.
Then someone told me I needed to go 1/4- 1/2 turn PAST contact with the shellplate, with the die- so that the press cams over hard- and takes all the slack out of the press.
Worked like a charm. Got my .002 shoulder bump...
Suggest you do the same. Screw in your sizing die another 1/4-1/2 turn past contact so you get a solid, hard cam over.