With Weatherby Mags. you have to use Weatherby brass.. It is from the way the brass is shouldered. With the cheaper Weatherby's like the Vangaurds, you can use off the shelf stuff, but the Weatherby Mags. you have to use theWeatherby brass.. Now thats what Weatherby told me when I started reloading my .240 Weatherby Mag., plus what the owners manual, and everything eles I've read about them..
Hunterman(Tony)