Funny, I have this problem with my 300 Weatherby. It's the only round I've ever had this problem with. It doesn't matter who's brass I use or what die. I have to bump the shoulder as extra .005". I know it doesn't sound like a lot, but it's enough that I can only get 4 reloads out of the brass if I don't anneal. Unfortunately, when I started reloading 40 years ago, we didn't all this knowledge at our fingertips and I had to learn the hard way. The 300 was also the reason I started reloading. As a 13 year old, I couldn't afford Weathby's ammo prices.