Just use an RCBS Pilot/Neck Reamer. When I think a donut is forming, I just size then run this pilot/reamer into the neck. It's designed to replace the pilot on the RCBS Trimmer lathe cutting tool. A touch of neck turning lube, a couple of turns while Trimming, and "donut? What donut?Im surprised you don't neck turn your brass- Im worried about a "donut" forming inside the brass screwing up the amount of grab on the bullet.
FWIW, most bullets are seated far enough out that the pressure ring (where the bearing surface meets the boat tail) is above it. Only time the donut is a real issue is when seating a Loooong bullet and you have to stick a lot of it into the case so you can chamber it.