I have had the same problem 4seventy mentions except it was a Model 70 458.

In staggered feed magazines the 458 Win and 458 Lott when loaded with blunt bullets are a bit like the WSSMs, that is, they are always on the verge of jamming and especially if the bolt is really rammed forward quickly.

A CRF is especially critical because if there is too much resistance to the case rim sliding up under the extractor the round will tip slightly and then you have the bullet catch the edge of the chamber.

Mike