Laker: Are you camming over with the FL die?
Set it up to contact the top of the shell holder with the ram fully up. Then, turn the die down another 1/2 turn (maybe a bit more). Run the case in and until you feel contact and then lean on the handle and you will feel it "bump" down further.
They should chamber fine.
It had been a couple of years recently since I had to make any new brass, and I forgot to do this myself. Got to the range with a bunch of COW loads and nothing chambered.
I knew right away what I had done, so took them home and cammed them all over. They now fit fine.
