Update: I tried a regular 260 Rem sizing die, and it did not solve the problem. Same thing: by the time I stop getting a very sticky bolt when I chamber the resized brass, the should is pushed way to far back.

Using Elkbane's advice I drew four lines the length of a resized case, popped it into the chamber, and forced the sticky bolt open and closed on it five or six times. The lines showed NO WEAR anywhere at the neck and shoulder, but all four lines showed wear about 1/2" above the head of the case, just above the webbing. I started a new post on this in the reloading forum (and now I see this one has been moved to reloading as well) describing this, and asking for advice. Custom dies, or have the chamber honed a bit wider?

I'm looking forward to reading your advice but won't be able to reply for a few days as my wife and I are taking the boys on a 12 mile hike into the mountains, hoping to get them their first black bear. The weather looks great, and summer has finally returned to Alaska!