Big bulls,
What you say is true "untill" the first shot is fired!! From that point on "that" case will headspace on the "shoulder" "IF" it's resized properly!! This is why the cases are made so sloppy to begin with. The ammo companys can let the belt take care of the head space the first time around!
I've loaded 10 of thousands of belted magnums over the years, and what i've seen is just what akbound said in his last post. "If" you want your brass to last, you DON'T push that shoulder back and let it head space on the belt! The belt becomes usless!!
One last thing: In my last post i was refering to modern belted magnums, not the "origional" ones like the H & H's. I'm not quite old enough to have been around when the H & H's came on the scene! :>