If the factory rounds chamber and you are confident that everything is safe (remove bolt and look through the chamber), try firing a single round (or maybe 2 or 3) and compare the cases.  There were many who "improved" the Krag case over the years, not just Ackley.

Look carefully at the markings on your FL die.  Might it be a Neck Sizing die?  Make sure you have the right shell holder.  Make some careful measurements of the fired & resized cases.

If you are like me and have one of those ancient presses (Pacific or Herters) that Mr. Hosmer described, RCBS sells an adapter or replacement kit ($12.50, IIRC) that brings it up to date, +/-.