Jim,
I've fired my 26 Nosler almost 300 times now. It still shoots great, and there's only a hint of throat erosion visible through my bore-scope. Nosler reports that most people are getting at least 1000 rounds before requesting a rebarrel, and one went 1500. Based on what I'm seeing with my rifle, that sounds about right.
The 6.5-.300 Weatherby has just about exactly the same case capacity, though the long "freebore" throat allows a little more velocity. If anything, I'd expect the freebore to extend barrel life. I've fired my rifle around 100 times, and can't be sure I'm seeing any erosion in the bore-scope.
