Wish I had seen your post earlier....
Despite what the die manufacturer's say- screwing down the sizing die until it "touches" the shellplate- that often doesn't provide any- or enough- shoulder bump.
I had a similar issue when I first started reloading. Posted on the 'Hide, and most guys were telling me to send the die back to Hornady for grinding. I'll add that I had a Hornady Headspace Gauge (which you need to get if you don't have one, it's the only way to know how much bump you're getting compared to your fireformed cases) so I KNEW I wasn't getting the shoulders bumped back.
Finally someone posted as I'm doing, saying "been there, done that", and to go 1/2 turn PAST contact with shellplate to take all slack out of the press and get firm contact with the die and shellplate.
Problem solved. Keep in mind that, as Bart said, we're only talking about a mere thousandth of an inch or two...and getting that press to cam over HARD is often the solution to the problem. Like I said, if you don't have the LNL headspace gauge, it's a must have. I don't know how anyone can reload without it.