I recently bought a rifle chambered for a wildcat AI (6.5/250 Sav AI) and discovered first hand what a donut is. And I didn't have any coffee on hand either.
I had full length resized previously fired (and fire-formed) brass and tested if they would chamber. No problems. The brass was fire-formed from .22-250 Lapua brass
I used a modified case with my Stoney Point OAL tool to find the rifle lands and seated some loads about 0.010" short.
I didn't test again for chambering until I was out at the range where I discovered that the bolt wouldn't close on loaded rounds.
I didn't know about donuts and it took me a good part of this morning to discover the donut at the juncture of the neck and shoulder.
Now it's decision time to either break down my loads and turn necks, or just re-chamber to 260 Rem and not have to fire-form brass in the future.
