";steps += "1. Projectile flight time to " + tr + " yards: ~" + t_target.toFixed(4) + " seconds.
";steps += "2. Kinetic energy loss: Initial " + Math.round(energy_constant) + " ft-lbs reduced to " + Math.round(energy_target) + " ft-lbs due to air resistance (G1 BC: " + bc + ").
";steps += "3. Gravity effect: Bullet fell " + drop_target.toFixed(2) + " inches from the bore line.
";steps += "4. Sight Compensation: Line of sight starts " + sh + " inches above bore, angled up to cross path at " + zr + " yards.
";steps += "5. Final Result: Bullet impact is " + Math.abs(final_impact.toFixed(2)) + " inches " + (final_impact < 0 ? "BELOW" : "ABOVE") + " point of aim.";document.getElementById('stepsOutput').innerHTML = steps;document.getElementById('stepsOutput').style.display = 'block';} else {document.getElementById('stepsOutput').style.display = 'none';}}
Using the Ballistics Calculator
A ballistics calculator is an essential tool for marksmen, hunters, and competitive shooters who need to predict the flight path of a projectile. By entering specific variables about your firearm and ammunition, you can determine exactly where a bullet will strike at various distances, accounting for gravity and air resistance.
To get the most accurate results, you will need high-quality data from your ammunition manufacturer or, preferably, data gathered from your own chronograph testing.
- Muzzle Velocity (fps)
- The speed of the bullet as it leaves the barrel, measured in feet per second. This is the primary driver of trajectory flatness.
- Bullet Weight (grains)
- The mass of the projectile. Heavier bullets typically retain energy better but may have more initial drop due to lower muzzle velocities.
- Ballistic Coefficient (BC)
- A measure of how well the bullet cuts through the air. A higher G1 BC indicates a more aerodynamic bullet that resists "drag" more effectively.
- Sight Height (inches)
- The vertical distance between the center of your rifle's bore and the center of your optical scope or iron sights.
How External Ballistics Works
When a bullet leaves the muzzle, two primary forces act upon it: gravity and drag. Gravity pulls the bullet toward the earth at a constant acceleration ($9.8 m/s^2$ or $32.174 ft/s^2$), while air resistance (drag) slows the bullet's forward velocity. The ballistics calculator uses these physics principles to plot the "trajectory."
Kinetic Energy (ft-lbs) = (Weight in Grains × Velocity²) / 450,437
The "Path" result is the most critical for shooters. It represents the vertical distance between your Point of Aim (what you see through the scope) and the Point of Impact (where the bullet actually hits). Because the scope is mounted above the barrel, the barrel is actually angled slightly upward to allow the bullet to "arc" into the line of sight at your "Zero Range."
Calculation Example: .308 Winchester
Scenario: A hunter is using a .308 Winchester with 150-grain bullets, zeroed at 100 yards. They want to know the drop at 300 yards.
Step-by-step solution:
- Muzzle Velocity: 2,800 fps
- Bullet Weight: 150 gr
- BC (G1): 0.420
- Zero Range: 100 yards
- Target Distance: 300 yards
- Calculate: The bullet takes approximately 0.35 seconds to reach 300 yards. In that time, gravity pulls it down significantly. However, since the rifle is zeroed at 100 yards, the barrel is angled to compensate for the first 100 yards of drop.
- Result: At 300 yards, the bullet will impact approximately 13.5 inches below the point of aim.
Common Questions
What is the difference between G1 and G7 BC?
The G1 Ballistic Coefficient is based on a flat-based projectile shape, common in older bullet designs. G7 is more accurate for modern, "boat-tail" long-range bullets. Most manufacturers provide G1 values as they appear higher and more attractive, though G7 is technically superior for long-range precision.
How does air temperature affect ballistics?
Colder air is denser than warm air. High air density increases drag, causing the bullet to slow down faster and drop more. While this ballistics calculator uses standard sea-level atmosphere, extreme temperature shifts can change your impact point by several inches at long ranges.
Why is Sight Height important?
Because the bullet starts below the line of sight (the scope), the relationship between the bore and the optic creates an offset. If you don't input the correct sight height, your "near zero" and "far zero" calculations will be slightly off, leading to misses at mid-range distances.