There are several different ways to ‘battle’ zero your rifle. Here is some info that may be useful. When we zeroed our M16’s back in the early 70’s with the issued 55gr projectile, the formula we used was:
25 yards – 1 inch low. This yielded 5.6 inches high at 100 yards and dead on at 250 yards. This was the Army method. I don’t know what the other services were using, but I understand that current Marine Corp zero allows for shots out to 600 meters with the ACOG. I expect that with a Mil-dot optic that would work for any projectile-launching platform. Again, back in the day we zeroed for a 55gr bullet, so the new green tips would require some tweaking. Anyway, here is some info I recently ran across on the web.