In addition to the info mentioned by JoeInCt, the Maryland AR15 Shooters Site includes a
Zeroing Methods section along with a variety of charts of
Zero Trajectories. Check out the Improved Battle Sight method: "It keeps the bullet within 2" of the point of aim from 8M to 220M."
According to Shoot v3.0 for XM193:
Set sights to shoot 0.71" High @ 100y Target for a 200y Zero.
Set sigths to shoot 2.55" High @ 100y Target for a 300y Zero.
. . . 1.44 Low @ 25y for a 200y Zero.
. . . 0.98 Low @ 25y for a 300y Zero.