Originally Posted by Chet Punisher
...But going between a .223 and a .308 I don't think I could get away with that, right?
It won't matter. The zero is going to be different for both rifles; the key is to know with a fair level of certainty that the difference between the two will remain relatively constant. Once you know where each rifle zeroes, then it's just a matter of writing that down. Then a shot or two will get you to perfect zero after a rifle swap each time.