You would have to set the barrel back quite a ways on a .300 WM to eliminate it's larger shoulder interfering with the body taper of the .300.
: So - .308, .30/06 or .300 Savage could all be re-chamberd, then the additonal work done to the bolt face, extractor, and action rails for feeding.
: Any standard or magnum rifle can be re-barreled to .300 mag as long as the action is long enough.