Bore Axis
Definition
The centreline of the barrel through which the bullet travels. The starting reference line for measuring gravity drop and the elevation difference from the line of sight.
- Definition
- Centreline of the barrel along the bullet's travel path
- Reference for
- Measuring gravity drop and sight-line offset
- Related concept
- Line of sight, offset above or below the bore axis
- Field
- Ballistics, external trajectory reconstruction
Common questions
Why does the bore axis matter for trajectory reconstruction rather than just the sight line?+
A bullet leaves the barrel travelling along the bore axis, not the sighting line the shooter used to aim, and the two are offset by the height of the sights above the barrel. Reconstructing where a bullet actually went requires starting from the bore axis and applying gravity drop, not from the aim point alone.
How does the bore axis relate to zero range?+
Zero range is the distance at which the bullet's path, launched slightly upward relative to the bore axis to compensate for gravity drop, crosses the sight line. Before and beyond that crossing point the bullet's height relative to the aim point differs, and the bore axis is the baseline from which the whole path is measured.
Related terms
- Ballistic Solver
- Software (JBM Ballistics, Strelok Pro, Hornady 4DOF, AB Quantum) that computes trajectory accounting for drag, BC, muzzle velocity, and atmospheric conditions. Supplementary...
- Battle-Sight Zero (BZO)
- The zero range selected by a military or paramilitary organisation as the standard setting for field use. US Army M4: 300 m....
- Gravity Drop
- The vertical distance a bullet falls below the bore axis at a given horizontal range, accumulating continuously from the instant of muzzle...
- Near-Zero Crossing
- The shorter of the two distances at which the bullet's trajectory intersects the line of sight. For a rifle zeroed at 300...
- Point-Blank Range (PBR)
- The maximum distance at which the bullet stays within the vital-zone radius above or below the line of aim without the shooter...
- Trajectory Rod
- A rigid fibreglass or aluminium rod inserted through a bullet wound channel and aligned with the channel geometry to define the bullet's...
- Vital Zone
- The defined target area used to compute point-blank range. For human thorax: typically 20 cm diameter (10 cm radius) centred on the...
- Zero Range
- The horizontal distance at which the bullet's trajectory crosses the line of sight. At this range, the point of aim and point...