When I was sizing 6mmBR brass up to 30BR , what had been a portion of the shoulder became the bottom of the neck.
Had I been loading bullets that seated their base below the neck/shoulder junction, I would have had a problem with the doughnut.
I turned all the necks for uniformity as I had a tight neck chamber and the excess was trimmed off neatly, including the doughnut.

"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