yep, neck sizing is the way to go with a belted (or non belted) case. I use the Lee Collet die in my 300 Weatherby and have had excellent results.
What sometimes happens with hot loads and an "oversized" chamber is that the case just ahead of the belt grows to belt diameter. When this occurs, the case will not chamber properly and there is no way a reg. FL sizer die will squeeze down this area.
There is a company that sells a collet sizer to size just in front of the belt. Personally, my cases wear out in other areas long before the case gets "fat".
Weatherby cases are more likely to stretch then cases with a conventional shoulder. Watch your pressures and your cases will give you good life.
With proper sizing, a belted case is every bit as accurate as a non belted case. Just look at the 1000yd results.
Good luck...
Jerry