When I measured my headspace with the 300 elite hunters, I came up with 3.915?My Load: 300 Berger Elite Hunter, 91gr H1000, Lapua Brass, Fed215M Primers = 2851 FPS.
Depending on your chambering, you should find a load somewhere between 90-92 grains. I'd start around 88-89 and go up until you hit pressure. For me, my accuracy was found at .015 off, which for me is 2.989" BTO.