Boresighting aligns an aiming device with a prescribed offset from the bore axis so the first live-fire group is likely to land on the zero target. It saves time and ammunition, but it is only an initial alignment. Live fire is still required to establish and confirm the zero.
Reference note: The original article described a 10-meter boresight and 25-meter zero from 2017-era Army guidance. Distances, offsets, targets, and confirmation requirements depend on the current manual, weapon, sight, ammunition, and selected zero.
Line of Sight and Bore Axis Are Separate
The line of sight runs from the shooter’s eye through the aiming device toward the aiming point. The bore axis is an imaginary line through the center of the barrel. Because a rifle’s sights sit above the bore, these lines begin vertically separated.
The Bullet Does Not Rise on Its Own
Gravity begins acting on the projectile as soon as it leaves the muzzle. The apparent “rise” relative to the line of sight occurs because the bore is angled slightly upward relative to that line. The projectile can therefore start below the line of sight, cross it, travel above it for part of its flight, and later fall through it again.
The actual trajectory is affected by muzzle velocity, ballistic coefficient, sight height, atmosphere, and other variables. It is not a perfect geometric parabola, particularly when aerodynamic drag is considered.
What an Offset Target Represents
At very short distance, the sight line and bore axis should not necessarily meet. A prescribed offset target represents the separation and angular relationship required for a particular weapon-and-sight combination. Aligning both indicators to their specified locations approximates the orientation needed to place the first live rounds on the later zero target.
Why Boresight at Short Distance
A short, controlled distance is practical for arms rooms and training areas and magnifies angular alignment enough to make a repeatable check possible. The exact offset matters: simply placing the bore laser and optic on the same point at 10 meters can produce the wrong relationship.
Why the Short-Range Zero Must Be Confirmed
A 25-meter target may simulate the expected point of impact at another distance, but it depends on assumptions about the system. Live-fire confirmation at the required distance tests those assumptions and exposes errors caused by ammunition, sight height, adjustment values, environmental conditions, or shooter input.
A Disciplined Sequence
- Inspect the weapon and aiming device.
- Use the correct boresight device, offset target, and prescribed distance.
- Align the bore indicator and sight to their separate reference points.
- Remove the boresight equipment and prepare the weapon for live fire.
- Fire and evaluate complete groups at the initial zero distance.
- Adjust from the group center using the sight’s documented values.
- Confirm at the required distance and record the final setting.
Boresighting is successful when it reduces the work needed to begin live-fire zeroing. It should never be treated as proof that the rifle is zeroed.