Just an additional comment, but it is not out of the question that Hornady may have had a bad run of brass. I've seen one run of brass totally throw off a test and have degreed mechanical engineers, scratching their heads about pressure issues. Turns out the brass was too soft, and as a coincidence it was Hornady/Frontier brass. Everyone was looking somewhere else for the culprit of the pressure problems, assuming the brass was good because it was virgin.

These symptoms certainly tells me something may have happened during the production cycle, but at least Hornady is standing by their product and investigating and replacing the OP's ammo.

JMTCW..