Blr243 wrote:If the donut is pushed back out towards the outer case as the expander ball is drawn up when sizing , do we then have ok internal dimensions and no unnecessary potential pressure spike ftom too much bullet grip , or does chambering the round push that donut tight against the bullet ?
All of the above...... but if you use bushing dies the donut stays inside and then you don't get resistance on the bolt and with this die is the easy way to check for a donut just slide a bullet in a fired case and if you have them it will stop when it touches it at the bottom of the neck .
Now if you don't need to seat that deep there is no problem but if you do all of the above that blr243 has asked can happen.