You can neck the .308 down, but the 6.5 Creedmore actually has a little longer case. Won't make much difference in performance, but better check to see if they'll function in a gas gun. Something to mess with if you want. I've got an AR-10 in .308. Most of my loads are for 169gr. or up to 200gr. But I have a decent muzzle break that tames those loads down. If I load 147gr. for screwing around, recoil is pretty mild.