Quote Originally Posted by jim_k View Post
Just my experience, but I had new brass in a .300 Win Mag that I traded in, so I no longer have it. Fired new factory ammo, but can't remember the brand. Sized it based on headspace as noted by poster above, and fired a couple of times in my rifle. No used brass, and no other rifle. Then I could not chamber it, and almost got a live round stuck in the chamber (no bueno). Checked the brass with the gauge on the Larry Willis die, and it was too wide. Ran it through the die, and no problem after that. YMMV.
Now that you bring it up. I've only owned 300 winmags made by Savage and their headspace is always good. This might not be the case with all manufacturers and if there is too much HS between the belt and chamber (even tho the HS between the shoulder and chamber is good) will lead to the bulge.

I guess I've just been lucky.