Sorry I'm so late gettinginto this thread and hope the OP is still watching. First thing is that you are in an Axis forum and a lot of the info above, even your own, is for other models. You really have to watch the model numbers. Second, there are basically short action cartridges and long action cartridges. To say that the 308 is basically a 30.06 but shorter is way off the mark. The 308 is a short action cartridge while the 270 is a long action (i.e. magnum). 800 yards accurately with a 308 is stretching to say the least. The only short action I would try for that distance is a 243 - with a 95 grain bullet is has very close to the same trajectory as a 270.

Oh, and back to the Axis forum issue, if you want accuracy to 800 yards you nee to move away from the Axis and into something like a Model 11.