On my A2 I set the rear drum to 8/3 minus 2 (1 moa clicks). Then zero at 50/200 using the front sight post for elevation correction.
On the carbine, 6/3 minus 4 (half moa clicks). Then zero as above.
If you cannot get minus 2 or minus 4 clicks, you can loosen the set screw on the elevation drum and rotate/retighten to get there.