I appreciate the input trickymisfit. Oddly, my doughnuts developed after one sizing, and I was full length sizing with a standard RCBS die. I am only bumping the shoulder a few thousandths, and I retired some Rem brass after 12 firings using the same die settings with no problems. Did a lot of research online and got several hits with similar results using the Nosler brass, not sure why. Maybe too soft? I reamed the necks with a Wilson reamer, polished them, and got my groups back to normal. All the same, I ordered some Lapua brass and I think I'm gonna go with the Redding Type S match set. It seems, from my reading, that the doughnut issue is inherent to the 260, so I may have to fight it in the future.