Zeroing

Zeroing is the process of aligning a sighting device so that the shooter's point of aim coincides with the actual point of impact at a specified distance. It is commonly performed on firearms, particularly rifles with iron sights or optical scopes, but the term applies to any adjustable sighting system, including archery sights and some measurement instruments.

The goal is to account for the ballistic trajectory, muzzle velocity, and environmental factors so that aiming at the chosen distance results in a hit near the center of the target. The zero distance is the range at which the sight is calibrated to yield the intended point of impact. Choices vary with discipline and equipment; common options include close-range and longer-range zeros.

In practice, zeroing involves adjusting the sight's elevation and windage to bring the point of impact in line with the point of aim at the target distance. Methods range from using bore-sighting tools to confirm alignment before any live-fire, to live-fire confirmation at the zero distance. For scopes, turret adjustments move the reticle relative to the bore; for iron sights, the sights themselves are aligned to achieve the correct offset.

Key terms include point of aim (POA), point of impact (POI), reticle, turret, zero, and the units used to describe adjustments, such as MOA or milliradians (mrad).

Maintenance considerations include re-zeroing after changing ammunition, optics, or mounts. Weather, altitude, and temperature can also affect ballistic performance and may necessitate a recheck.