My brother in law has a 3-18x50mm VX-6 on a 300 Weatherby. The rifle is sighted in at 300 yards. We click and shoot all the way out to 500 yards, and the tracking does fine. When we track all the way back to zero, the 300 yard shot is always low when we set the turrets back to zero. Does anybody have problems with the VX-6 tracking? Is it not a reliable scope for long distance shooting?