I have a Weatherby Mark V in .257 Weatherby that the barrel is in question. I have posted on the reloading forum concerning fouling and casting the chamber to see if I have a throat left in the gun. Just starting to play with thoughts. What magnum calibers could a guy have the gun re-barreled/re-chambered to with this action without a lot of modifications except the new barrel?

An eroded throat is pretty easy to see after cleaning the barrel. You can also feel a rough throat after cleaning it when pulling a bronze brush back out of the affected area.

If I had a Weatherby with a worn out throat I would consider having them rebarrel it. Any of their cartridges from the 257, 270 and 7mm Weatherby should work from the magazine.

the bolt face is the same up to the 340wthby I think.

My dad just sent his to have it rebarrelled with a Pac-Nor tube and he really likes it.

you could rebarrel to
.257 Weatherby again
.264 Win Mag
.270 Weatherby Mag
7MM rem mag or Weatherby mag
300 Win mag
.338 Win mag.
.375 Taylor
.416 Taylor
.458 Win Mag

All have the same bolt face and the .300 and .340 Weatherbys are too long for that action I think.