Check the sides of the fired case/s for dimples or a frosted look, these can indicate what the chamber walls look like.
Check the base of the case for signs of the ejector impacting or the hole the ejector fits into.
Smoke or use some black marker on the bullet, chamber the cartridge then extract unfired. Look for signs the bullet is making contact with the rifling.
It’s a weatherby. I don’t think the throat is the issue.