RR has it, your seating die is not set up correctly.
Back the seating die way out of the press.
Place a sized case in the shell holder and raise the ram.
Screw the seating die into the press until you feel it contact the case.
Lower the ram and back the seating die OUT at least one full turn.
Lock the die down with the locking nut.
Adjust seating depth with seating stem.