A 308 will only need around 35moa to get to 1000, so you should have more than enough using a 0moa base, even if your scope is optically centered. If you think you might shoot farther then get the 15 or 20moa. With that much adjustment available it should still zero at 100(my SIII with 70moa adj zeros at 100 with a 20moa farrell base, but it is close).
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