I've been loading Weatherby cartridges with Norma (Weatherby) brass for over 30 years. Can't seem to remember this as an issue. If anything, it was loose primer pockets after about five (?) or so firings.
That's been my experience as well, but within the past 20 years haven't encountered many loose primer pockets either with Weatherby (Norma) brass. And I've loaded for the .240, .257, 6.5-.300, .270, 7mm, .300 and .340 Weatherby Magnums.
