I don't load the 300 wby, but I do load the 300WSM and had a similar problem. I loaded on the upper levels but not too hot, neck sized and suddenly found hard sticky bolts around the 3rd-4th loadings of the same cases. I full length resized and that seemed to help ( I was trying to bump the shoulders back a little but I had trouble setting up the die in a hurry so I simply FL resized). I have heard several people feel it necessary to aniel the case necks after several loadings. I haven't tackled that task as of yet.
After repeated firing the case shoulders get stretched farther and farther forward and make the bolt work a little too hard to chamber the round.
Good luck, Mark.
I used to re-load but now I "hand-load".
-- Well, at least I try