First, make sure the sizing die is adjusted as follows: with the ram at the top of its stroke, thread the sizing die into the press until it makes contact with shell holder, lower the ram, and thread the sizing die in an additional 1/3 turn and tighten the lock ring. This ensures that the sizing die is bumping the shoulder back as well as reducing the diameter of the case. If the shell holder does not contact the base of the die, the diameter of the case is squeezed down, making the case (and distance to the shoulder) longer.
If this does not solve the problem, return the sizing die with two fired cases, and we can modify the die to fit to your chamber.
Our address is:
Lee Precision Inc,
4275 County Road U
Hartford, WI 53027
