Re: 300 WSM vs. 300 WM
That is the way you should resize almost any brass, headspace .002 off the shoulder. Forget about the belt.
For what it's worth, after a fair amount of experience with both, I prefer the 7 mag to a .300. It's pretty hard to beat a .284 180 gr Berger with its' .659 G1 BC. Sure you can go to the 210 gr .308 bullet for .631 BC, and no appreciable difference, but the extra 30 grains of bullet and heavier powder load make for stouter recoil. Not much maybe, but stouter.
In the end they are close enough that I don't believe an elk is going to know the difference at any range.
I would go with a .338 and super high BC's if I thought I needed more than what my 7mm delivers.