Low tech annealing is done with a propane torch, a metal bucket and a brick or two. You really do not need the spinning.  put the bricks in the bucket.  Add water until the upper surface of the brick is just above the water line. Put a Krag case on the brick, neck up, of course.  Turn out the lights.  Light the propane torch.  Using as little flame as you can, heat the neck until it starts to turn color.  Remove flame & tip the case into the water.  Best to use a stick to tip the case.  It is hot.  If you see the neck get red hot, you have gone too far.

I agree maybe your sizer die is squeezing the neck too much.  Or maybe the expander button is too big.