Hey PJ .........
Have you taken the die out of your Dillon, then threaded the die thru the tool head and then put the nut on the bottom side of the tool head?? If you've already tried that go back to plan A.
OOPS. I just re-read your missive. My solution was for a die that is too short to reach thru the tool head. Or, depending on cost, I might suggest a Redding Profile Crimp die and go to a separate crimping step. While I have had excellent results with RCBS Cowboy dies, I have come to prefer separate seating and crimping. Just me.
Coffinmaker