Wow, talk about a mouthfull....

Where to begin...I think the bullet/projectile diameter thing has been covered. Although, truth be told, you're taking your own life in your hands if you're shooting .308 bullets loaded in a .30-06 case, because it seems that you are refering to the cartridge .308 win bullet instead of .308" bullet which would be correct. The .308 win shoots a .311" bullet, which would create HIGH PRESSURES when fired out of a .30-06 case into a .300/.308 (lands/grooves) barrel.

THe .308 round will load in a .30-06 because the .308 winchester was designed with the .30-06 case as a template/starting off point...the rebated rim is the same dimensions, so it will feed just fine, but WILL NOT HEADSPACE, meaning that the neck and shoulder of the cartridge is not contacting anything at the chamber mouth. It seems that on occasion one will fire and be just fine, but it isn't going to happen in my gun, I'll guarantee you that!!!

Screw the 10 ring, keep them in the zero!!!