What are common issues with zeroing a first focal plane scope?

Parallax Issues

Parallax errors arise when the shooter’s eye position changes, affecting the reticle’s alignment with the target. To mitigate this, shooters should ensure their eye is centered behind the reticle and the scope’s parallax adjustment is set to zero. For most scopes, this is achieved by looking through the scope and adjusting the parallax knob until the reticle is sharp. It’s recommended to adjust the parallax at the magnification range most commonly used for the intended application.

Windage and Elevation Adjustments

Since first focal plane scopes display the reticle markings at the actual bullet trajectory, windage and elevation adjustments require precise calculation. Shooters need to account for bullet drop and wind deflection at varying magnifications, which can be complex and time-consuming. A common technique is to create a ballistic profile using a ballistic calculator or shooting software to determine the necessary adjustments. For example, at 1000 yards, a 308 Winchester bullet may drop 10.9 inches at 500 yards and 22.9 inches at 1000 yards. Shooters must apply these corrections to their first focal plane scope’s adjustments.

Long Range Calibration

Long range calibration of a first focal plane scope requires patience and attention to detail. Shooters should start by calibrating the scope at 100 yards, then gradually move to longer ranges, adjusting the windage and elevation accordingly. It’s essential to use a high-quality ballistic calculator or shooting software to determine the necessary adjustments. For example, at 1000 yards, a 308 Winchester bullet may have a 45-minute wind drift at 15 mph. Shooters must apply these corrections to their first focal plane scope’s adjustments to achieve accurate long range shooting.