Open up Virtual Arsenal and equip the MK-1 (Preferably with one of the sights listed above and a bipod for stability)
Set zero to 1000m and engage the VR Soldier at 1000m. Watch as the rounds pass over his head. Now set zero to 900m and engage. Now you should be hitting him.
You can repeat this process for targets past 1000m, or from 1000-600m. At 500m and below, the zero should be correct.