Weatherby’s are works of art and precision machining.
I helped a local gunsmith diagnose problems with an excellent custom copy of 257 Weatherby. Getting reloads that function is not automatic. Has to do with neck down transition shape and incredible precision of the base and lower part of the cartridge. Requires excellent dies and strong press.
In the beginning he could not get the bolt to close on the reloads. It is not an uncommon problem.
Doesn’t that cartride headspace on the belt? Is it a resizing issue at or near the case head? Just wondering why the neck would be such an issue, but then I really know very little about this cartridge.