I have read various articles in the past reference people making various changes so that their belted magnums head space at the shoulder rather then at the belt. It was more idle curiosity then anything else. I assume it was just to have more control on the head spacing of the cartridge. During a conversation with Jim Carstensen when ordering a couple of FL resizing dies (one of which is for my 300 win mag) head spacing came up and he said that he could fix the die so that the resulting cases would head space on the shoulder. What do I actually gain by doing that?