Ditto what olddav said. Case mouth tension is what holds a bullet in place, not the crimp. You are probably over expanding. Go back to your instructions for setting the expander die. Do just enough to be able to sit the bullet into the case mouth to keep it steady.
When the bullet seats deeper into the case when you chamber it, that's called "bullet setback." After you seat the bullet, do a very light crimp. This isn't really a crimp, but just removing the slight "flare" you created when you expanded the case. When done, take the completed round and push the nose of the bullet against your work bench, trying to push the bullet into the case. You shouldn't be able to. If you can, your settings are off. Get back to basics and you'll be fine.
If you want to shoot...shoot...don't talk! Tuco
USAF Munitions 1969-1992