I'm loading for a 30BR, necking up from 6mmBR.
Yep there is a definite doughnut, as the top of the shoulder is now the bottom of the neck.
I'm turning for a tight neck chamber anyway so it's easily turned off while I"m there.

30-06 to 35whelan or 338-06, never had a doughnut problem.

"Camping places fix themselves in your mind as if you had spent long periods of your life in them.
You will remember a curve of your wagon track in the grass of the plain like the features of a friend."
Isak Dinesen