Bullet Drop Calculator

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Bullet Drop Calculator

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Enter values and click "Calculate Bullet Drop".

function calculateBulletDrop() { var muzzleVelocity = parseFloat(document.getElementById('muzzleVelocity').value); var ballisticCoefficient = parseFloat(document.getElementById('ballisticCoefficient').value); var targetRange = parseFloat(document.getElementById('targetRange').value); var zeroRange = parseFloat(document.getElementById('zeroRange').value); var sightHeight = parseFloat(document.getElementById('sightHeight').value); var resultDiv = document.getElementById('result'); // Input validation if (isNaN(muzzleVelocity) || muzzleVelocity <= 0) { resultDiv.innerHTML = 'Please enter a valid Muzzle Velocity (must be a positive number).'; return; } if (isNaN(ballisticCoefficient) || ballisticCoefficient <= 0) { resultDiv.innerHTML = 'Please enter a valid Ballistic Coefficient (must be a positive number).'; return; } if (isNaN(targetRange) || targetRange <= 0) { resultDiv.innerHTML = 'Please enter a valid Target Range (must be a positive number).'; return; } if (isNaN(zeroRange) || zeroRange <= 0) { resultDiv.innerHTML = 'Please enter a valid Zero Range (must be a positive number).'; return; } if (isNaN(sightHeight) || sightHeight < 0) { resultDiv.innerHTML = 'Please enter a valid Sight Height (must be a non-negative number).'; return; } // Constants var g_inches_per_s2 = 386.088; // Gravity in inches/second^2 (32.174 ft/s^2 * 12 in/ft) var yards_to_feet = 3; var moa_at_100_yards = 1.047; // 1 MOA at 100 yards in inches // Simplified G1 drag constant. This is an approximation. // A full ballistic solver would use a more complex drag model. var G1_DRAG_CONSTANT = 1000; // Function to calculate Time of Flight (TOF) and Drop below bore line function calculateBallistics(range_yards, mv_fps, bc_g1) { var range_feet = range_yards * yards_to_feet; // Initial TOF without drag var tof_no_drag = range_feet / mv_fps; // Simplified drag factor based on G1 BC // This factor increases TOF due to air resistance var drag_factor = range_yards / (bc_g1 * G1_DRAG_CONSTANT); // Adjusted TOF considering drag var tof_adjusted = tof_no_drag * (1 + drag_factor); // Drop below bore line due to gravity var drop_bore_line_inches = 0.5 * g_inches_per_s2 * tof_adjusted * tof_adjusted; return { tof: tof_adjusted, drop_bore_line: drop_bore_line_inches }; } // Calculate ballistics for target range var targetBallistics = calculateBallistics(targetRange, muzzleVelocity, ballisticCoefficient); var dropAtTargetBoreLine = targetBallistics.drop_bore_line; var tofAtTarget = targetBallistics.tof; // Calculate ballistics for zero range var zeroBallistics = calculateBallistics(zeroRange, muzzleVelocity, ballisticCoefficient); var dropAtZeroBoreLine = zeroBallistics.drop_bore_line; var tofAtZero = zeroBallistics.tof; // Calculate bullet path relative to the line of sight (LOS) // Y_bullet_relative_to_bore = -drop_bore_line (negative because drop is below bore) // Y_LOS_relative_to_bore = sightHeight + (range / zeroRange) * (drop_at_zero_bore_line – sightHeight) // Bullet_Path_LOS = Y_bullet_relative_to_bore – Y_LOS_relative_to_bore var bulletPathLOS_inches = (-dropAtTargetBoreLine) – (sightHeight + (targetRange / zeroRange) * (dropAtZeroBoreLine – sightHeight)); // Calculate MOA adjustment // A negative bulletPathLOS_inches means the bullet is below LOS, requiring "come up" (positive MOA adjustment) // A positive bulletPathLOS_inches means the bullet is above LOS, requiring "come down" (negative MOA adjustment) var moaAdjustment = bulletPathLOS_inches / (targetRange / 100 * moa_at_100_yards); var adjustmentDirection = ""; if (moaAdjustment 0) { adjustmentDirection = "Come Up"; } else { adjustmentDirection = "No Adjustment"; } resultDiv.innerHTML = 'Time of Flight to Target: ' + tofAtTarget.toFixed(3) + ' seconds' + 'Bullet Path Relative to LOS: ' + bulletPathLOS_inches.toFixed(2) + ' inches ' + (bulletPathLOS_inches < 0 ? '(Below LOS)' : '(Above LOS)') + '' + 'Vertical Adjustment: ' + adjustmentDirection + ' ' + moaAdjustment.toFixed(2) + ' MOA'; } .calculator-container { background-color: #f9f9f9; border: 1px solid #ddd; padding: 20px; border-radius: 8px; max-width: 600px; margin: 20px auto; font-family: Arial, sans-serif; } .calculator-container h2 { text-align: center; color: #333; margin-bottom: 20px; } .calculator-inputs label { display: block; margin-bottom: 5px; color: #555; } .calculator-inputs input[type="number"] { width: calc(100% – 22px); padding: 10px; margin-bottom: 15px; border: 1px solid #ccc; border-radius: 4px; box-sizing: border-box; } .calculator-inputs button { background-color: #007bff; color: white; padding: 12px 20px; border: none; border-radius: 4px; cursor: pointer; font-size: 16px; width: 100%; box-sizing: border-box; } .calculator-inputs button:hover { background-color: #0056b3; } .calculator-results { margin-top: 20px; padding: 15px; background-color: #e9ecef; border-radius: 4px; border: 1px solid #dee2e6; } .calculator-results h3 { color: #333; margin-top: 0; margin-bottom: 10px; } .calculator-results p { margin-bottom: 8px; line-height: 1.5; color: #333; }

Understanding Bullet Drop: The Science of Trajectory

Bullet drop is a critical factor for anyone involved in shooting, from hunters and sport shooters to military and law enforcement personnel. It refers to the vertical distance a bullet falls due to gravity as it travels downrange. Understanding and compensating for bullet drop is essential for accurate shot placement, especially at longer distances.

What Causes Bullet Drop?

The primary force behind bullet drop is gravity. As soon as a bullet leaves the barrel, gravity begins to pull it downwards. While the bullet is traveling forward, it is simultaneously falling. The longer the bullet is in the air, the more it will fall.

However, gravity isn't the only factor. Air resistance (drag) also plays a significant role. Drag slows the bullet down, which in turn increases its time of flight. A longer time of flight means more time for gravity to act on the bullet, resulting in greater drop.

Key Factors Influencing Bullet Drop

  1. Muzzle Velocity (fps): This is the speed at which the bullet exits the barrel. Higher muzzle velocities mean the bullet reaches the target faster, reducing the time gravity has to act, and thus reducing bullet drop.
  2. Ballistic Coefficient (BC): The ballistic coefficient is a measure of a bullet's ability to overcome air resistance. A higher BC indicates a more aerodynamic bullet that retains its velocity better, leading to less drop over distance. The G1 model is a common standard for comparing BCs.
  3. Target Range (yards): As expected, the further the target, the more time the bullet spends in the air, and consequently, the greater the bullet drop.
  4. Zero Range (yards): This is the distance at which your rifle scope (or sights) is calibrated to hit the point of aim. At this specific range, the bullet's path intersects your line of sight. The zero range significantly impacts the bullet's trajectory relative to your line of sight at other distances.
  5. Sight Height (inches): This is the vertical distance from the center of your rifle's bore to the center of your scope's reticle. Because the scope sits above the bore, the bullet starts below your line of sight and must rise to meet it at the zero range. This initial offset is crucial for calculating the bullet's path.
  6. Gravity: A constant force, pulling the bullet downwards.
  7. Air Density: While not an input in this simplified calculator, factors like altitude, temperature, and humidity affect air density, which in turn influences air resistance and thus bullet drop.

How the Bullet Drop Calculator Works

This calculator uses a simplified ballistic model to estimate bullet drop. It takes into account the bullet's muzzle velocity, its ballistic coefficient (G1), the target range, your rifle's zero range, and the height of your scope above the bore. Here's a basic overview of the calculation process:

  1. Time of Flight (TOF): It first estimates the time it takes for the bullet to reach the target. This isn't simply distance divided by muzzle velocity, as air resistance slows the bullet down. The ballistic coefficient is used to approximate how much drag affects the bullet's speed and thus its TOF.
  2. Drop Below Bore Line: Once the TOF is estimated, the calculator determines how much the bullet falls due to gravity during that time, relative to the rifle's bore line (an imaginary line extending straight out from the barrel).
  3. Path Relative to Line of Sight: Finally, it adjusts this raw drop for your specific zero range and sight height. Since your scope is above the bore and you've zeroed at a certain distance, the bullet's path will cross your line of sight. The calculator determines if the bullet will be above or below your line of sight at the target range.
  4. MOA Adjustment: The result is then converted into Minutes of Angle (MOA), a common unit of angular measurement used in shooting to adjust scope turrets. A negative MOA indicates you need to "come down" (adjust your scope down), while a positive MOA indicates "come up" (adjust your scope up).

Using the Results for Accurate Shooting

The "Vertical Adjustment" in MOA tells you exactly how many clicks (or how much rotation) you need to apply to your scope's elevation turret to hit your target at the specified range. For example, if the calculator shows "Come Up 10.5 MOA", you would adjust your scope's elevation turret up by 10.5 MOA.

It's important to remember that this calculator provides an estimate. Real-world conditions (wind, temperature, altitude, bullet variations) can affect actual bullet drop. Always confirm your ballistic data with actual shooting at various ranges.

Limitations of This Calculator

This calculator uses a simplified ballistic model for ease of implementation. It does not account for:

  • Wind drift (horizontal movement due to wind)
  • Changes in air density due to altitude, temperature, or humidity
  • Spin drift (a small horizontal deflection caused by the bullet's spin)
  • Coriolis effect (negligible at most practical shooting ranges)
  • Specific G7 ballistic coefficients (it uses a G1 approximation)

For highly precise long-range shooting, more advanced ballistic software or dedicated devices are recommended. However, for general hunting and target shooting, this calculator provides a very useful and practical estimate for bullet drop compensation.

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