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Sounds to me like normal case neck tension is ironing out the soft polymer coating on the BCS rounds. Try loading a few with no crimp to see if they don't shrink, too.
The Lee Carbide Factory Crimp Die won't iron anything that doesn't rub the carbide sizing ring at its mouth, so try pushing a finished round up into the ring with your fingers. If it goes, you're not getting rubbing. It if resists, you are getting sizing action (any bullet will spring back out a little after being sized down, to the fact it went through the ring under the force of the press already should not make it small enough to pass through the ring freely).
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