Mostly COL. I believe, not postive, that the Norma is set to 3.3 inches and the Winchester is 2.8 inches. Same case but you have to seat the heavier bullets further into the case of the Winchester eating up powder room.
On a seperate note..
I wonder if you could put a small notch into the reciever (similiar to what's on Weatherby's ULW) and use a Wyatt extended magazine box. This should be able to get you out to 3.0 inches. Which is all the 6.5x284 should need on a hunting rifle. I don't even know if you need a notch cut or not, but 3.0 inches seems just about perfect to me. Short action but still able to seat all but the heaviest bullets out there.
