The P223 scope is calibrated for the 223/5.56 round. You will not be able to use the hold-over marks with a 308. They make a P-308 and M-308 scopes for the 308/7.62 rifles.
Millet, Weaver, ATK and U.S, Optics all make windage adjustable rings. They are available in 1", 30mm and 34mm. There are not any rings that I am aware of that are elevation adjustable. You would need to use the scopes elevation turret to adjust it.