Height Over Bore Calculator
Calculate your rifle’s mechanical offset and point-of-impact shift based on sight height and zero distance.
Formula: POI = HOB × (Distance / Zero) – HOB
0.00°
0.00″ Low
50 Yds
Visual representation of Line of Sight (Blue) vs Bore Path (Red)
| Distance (Yds) | Offset (Inches) | Status |
|---|
Note: These calculations assume a linear path for close-range offset. Ballistic drop will increase deviation at long ranges.
What is a Height Over Bore Calculator?
A Height Over Bore Calculator is a specialized ballistic tool used to determine the vertical distance between the axis of a firearm’s bore (the center of the barrel) and the axis of the sighting system (the center of the scope or iron sights). In the shooting world, this is often referred to as “mechanical offset.” This measurement is critical for understanding why a bullet strikes lower than the point of aim at very close distances.
Whether you are a competitive shooter using a height over bore calculator to master stage transitions or a tactical operator needing to understand your 10-yard offset for a 50-yard zero, this tool provides the mathematical clarity needed. Many shooters mistakenly believe the bullet rises out of the barrel; in reality, the barrel is simply angled upward relative to the sight line. Using a height over bore calculator helps you visualize and compensate for this geometric reality.
Height Over Bore Calculator Formula and Mathematical Explanation
The math behind a height over bore calculator relies on linear interpolation and basic trigonometry. At the muzzle (0 yards), the bullet is exactly one “Height Over Bore” (HOB) unit below the line of sight. As the bullet travels toward the zero distance, it “climbs” toward the line of sight.
The core formula used by our height over bore calculator for linear mechanical offset is:
Variables Explanation Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| HOB | Height Over Bore | Inches / mm | 1.5″ – 3.5″ |
| Zero Dist | Distance where POI = POA | Yards / Meters | 25 – 200 |
| Target Dist | Current distance to target | Yards / Meters | 0 – 50 |
Practical Examples of Height Over Bore Calculator
Example 1: The Modern Sporting Rifle (AR-15)
Imagine an AR-15 with a standard optic mount. The HOB is 2.6 inches, and the rifle is zeroed at 50 yards. If a shooter needs to take a precise shot at a target only 5 yards away, they use the height over bore calculator logic. At 5 yards, the formula yields: (2.6 * (5/50)) – 2.6 = -2.34 inches. This means the shooter must aim 2.34 inches high to hit the intended spot.
Example 2: Precision Bolt Action Rifle
A long-range shooter has a bolt-action rifle with a 1.5-inch HOB and a 100-yard zero. While checking the height over bore calculator for a 25-yard small game shot, the result is: (1.5 * (25/100)) – 1.5 = -1.125 inches. Even with a lower HOB, the offset remains significant enough to miss a small target if not accounted for.
How to Use This Height Over Bore Calculator
- Measure HOB: Measure from the center of your bolt/bore to the center of your optic’s objective lens.
- Enter Zero Distance: Input the yardage at which you performed your live-fire zero.
- Enter Target Distance: Input the distance you are currently curious about (e.g., 7 yards for CQB).
- Analyze Results: The height over bore calculator will instantly show your POI (Point of Impact) shift in inches.
- Review the Chart: Use the dynamic chart to see how your bore path converges with your line of sight.
Key Factors That Affect Height Over Bore Calculator Results
- Optic Mount Height: Higher mounts (like 1.93″ or 2.26″ mounts) significantly increase the HOB, requiring more drastic “hold-overs” at close range.
- Zeroing Distance: A shorter zero distance (e.g., 25 yards) means the bore is angled more steeply upward, causing the bullet to cross the line of sight faster.
- Barrel Length: While it doesn’t change HOB directly, it affects velocity, which impacts trajectory over long distances beyond the height over bore calculator‘s linear scope.
- Ammunition Velocity: Higher velocity rounds spend less time in the air, but the mechanical offset calculated by the height over bore calculator remains primarily a geometric factor at close range.
- Angle of Fire: Shooting at steep uphill or downhill angles can slightly change the perceived HOB, though this is usually negligible for mechanical offset.
- Sight Radius: On iron sights, the distance between front and rear sights affects how you perceive the bore axis, though the center-to-center measurement for the height over bore calculator remains the constant.
Frequently Asked Questions (FAQ)
No, every firearm has a Height Over Bore. Our height over bore calculator works for pistols, shotguns, and bolt-action rifles alike.
This is due to mechanical offset. The barrel is below the sights. The height over bore calculator shows exactly how much lower the barrel is pointing at that specific distance.
Yes. A higher HOB actually gives a slight ballistic advantage at very long ranges by providing a better “starting angle,” but it makes close-range shots harder.
Measure the diameter of your bolt and divide by 2. Measure the diameter of your scope tube and divide by 2. Then measure the gap between them. Add all three values for your height over bore calculator input.
Yes, as long as you are consistent. If you enter HOB in cm, the result will be in cm. If you enter distance in meters, keep zero distance in meters.
Most bolt actions are 1.5″ to 1.75″. Most AR-15s with standard mounts are 2.5″ to 2.7″.
No, this tool focuses strictly on vertical mechanical offset between the bore and the sights.
The hold-over is the amount you aim above your target to compensate for the offset shown in the height over bore calculator.
Related Tools and Internal Resources
- Comprehensive Ballistics Guide – Learn the physics behind bullet flight.
- Scope Mounting Tips – How to choose the right height for your optic.
- Zeroing Distance Chart – Compare 25, 36, 50, and 100-yard zeros.
- Long Range Shooting Basics – Fundamentals of precision marksmanship.
- MOA to MRAD Converter – Easily switch between angular measurement units.
- Bullet Drop Calculator – Calculate trajectory beyond the zero point.