A friend necks up 270 WSM and seats a bullet into the lands, adds a solid charge of 4350 and fire forms into 7WSM with no problems.
I neck down 300WSM brass to form a false shoulder, add 59.0grs 4350 with a 140 gr bullet and fire form with no problems.
The 7 is the only WSM I own so head stamp don't matter to me but I can see how it could be a problem owning more than 1 WSM.
