[sugarmaker]

I have 200 Hornady 500 S&W cases (large rifle version) that I can't seat primers into with my LNL-AP or rock chucker. I ran them across the dillon 600 set to max de-crimp (cases would just barely go into the tool) and I can now get them started but 2/3 won't seat in the press. I can seat them using a hand tool but I grit my teeth, they're so tight. Primers are CCI-250's or 8 1/2-120's, they work fine everywhere else. Never, ever had cases this tight, not even close.

Any tricks out there before I call Hornady?

[unknwn]

I would imagine that you have a pretty penny wrapped up in purchasing that brass.
I would be contacting Hornady for satisfaction.
If that fails you, I would:
First: use a decrimping set like the CH4D tooling set or the RCBS swaging set
The choice of tooling is because I would opt to decrimp by swaging the existing metal, NOT cutting any away.
Second: put each decrimped casing through a primer pocket uniformer using cutters like the RCBS Primer Pocket Uniforming cutting tools

The second operation would be to ensure that the primer pockets are of the proper depth and have an acceptable profile at the base of the pocket depth.
(square/perpendicular to the side walls & without an interfering radius at that point).
If the primer pocket is of an inadequate depth -or- has an unacceptable base depth profile, you have no other choice than to cut the excess material out of the depths of the primer pocket well.