Advanced Ballistic Coefficient Calculator
Ballistic Configuration
Basic BC
Advanced BC
Trajectory
Comparison
Environmental
Presets
Saved Setups
Projectile Details
Velocity-Dependent Ballistic Coefficients
Enter BC values at different velocity ranges for more accurate trajectory calculations.
Advanced Projectile Parameters
Trajectory Parameters
G1 Drag Model
Flat-based, 2 caliber (tangent) ogive
The G1 is the most common reference standard, used for:
Hunting Bullets:
0.200-0.450
Match Bullets:
0.450-0.550
High BC Bullets:
0.550-0.650+
G7 Drag Model
Long, boat-tailed, 10 caliber secant ogive
The G7 is optimized for modern long-range bullets:
Match Bullets:
0.150-0.220
Long Range:
0.220-0.270
Elite Long Range:
0.270-0.320+
Select bullets to compare the effects of different drag models:
Environmental Conditions
Adjust environmental parameters to see their effect on ballistic coefficient and trajectory.
Reference Conditions
Reference Atmospheric Data:
- ICAO Standard Atmosphere: 59°F (15°C), 29.92 inHg (1013.25 hPa), 0% humidity, sea level
- Army Standard Metro: 59°F (15°C), 29.53 inHg (1000 hPa), 78% humidity, sea level
The calculated density of air is used to determine the corrected BC value, which affects the projectile's trajectory.
Common Rifle Cartridges & Bullets
Environmental Condition Presets
Tactical Shooting Scenarios
Setup saved successfully!
Your Saved Setups
Match .308 175gr
Hunting Load 6.5 CM
Ballistic Coefficient Results
G1 Ballistic Coefficient
0.465
G1 BC
G7 Ballistic Coefficient
0.238
G7 BC
Form Factor
1.00
i
Sectional Density
0.253
lb/in²
Trajectory Chart
Trajectory Table
Comparison Chart
Calculations
Bullet Path
Wind Drift
Zero Line
0
100
200
300
400
500
600
700
800
900
1000
| Range (yd) | Velocity (fps) | Energy (ft-lb) | Drop (in) | Wind Drift (in) | Time (s) |
|---|---|---|---|---|---|
| 0 | 2700 | 2718 | -1.50 | 0.00 | 0.000 |
| 100 | 2564 | 2453 | 0.00 | 1.03 | 0.116 |
| 200 | 2436 | 2211 | -4.82 | 4.33 | 0.238 |
| 300 | 2312 | 1990 | -16.09 | 10.15 | 0.367 |
| 400 | 2193 | 1792 | -35.24 | 18.75 | 0.504 |
| 500 | 2078 | 1609 | -63.39 | 30.46 | 0.650 |
| 600 | 1969 | 1443 | -101.74 | 45.62 | 0.804 |
| 700 | 1864 | 1294 | -151.79 | 64.69 | 0.968 |
| 800 | 1764 | 1159 | -214.50 | 88.19 | 1.142 |
| 900 | 1670 | 1039 | -291.43 | 116.69 | 1.327 |
| 1000 | 1580 | 932 | -384.46 | 150.82 | 1.524 |
| Range (yd) | G1 BC Drop (in) | G7 BC Drop (in) | Difference (in) |
|---|---|---|---|
| 0 | -1.50 | -1.50 | 0.00 |
| 100 | 0.00 | 0.00 | 0.00 |
| 200 | -4.82 | -4.58 | 0.24 |
| 300 | -16.09 | -15.12 | 0.97 |
| 400 | -35.24 | -32.69 | 2.55 |
| 500 | -63.39 | -58.24 | 5.15 |
| 600 | -101.74 | -92.75 | 8.99 |
| 700 | -151.79 | -137.26 | 14.53 |
| 800 | -214.50 | -193.10 | 21.40 |
| 900 | -291.43 | -261.92 | 29.51 |
| 1000 | -384.46 | -344.83 | 39.63 |
1. Sectional Density Calculation
Sectional Density (SD) represents the ratio of a bullet's weight to its diameter squared.
SD = W / (D² × 7000)
Where:
- W = Bullet weight in grains
- D = Bullet diameter in inches
- 7000 = Conversion factor (grains per pound)
Calculation:
- SD = 168 grains / ((0.308 in)² × 7000)
- SD = 168 / (0.094864 × 7000)
- SD = 168 / 664.048
- SD = 0.253
2. Ballistic Coefficient Calculation
The Ballistic Coefficient (BC) is calculated using the following formula:
BC = SD / i
Where:
- SD = Sectional Density
- i = Form Factor (relative to standard projectile)
G1 BC Calculation:
- BCG1 = SD / iG1
- BCG1 = 0.253 / 0.544
- BCG1 = 0.465
G7 BC Calculation (Conversion from G1):
- BCG7 ≈ BCG1 × 0.512
- BCG7 ≈ 0.465 × 0.512
- BCG7 ≈ 0.238
Note: This is an approximation for typical boat-tail bullets. More accurate G7 values should be measured directly.
3. Environmental Corrections
Ballistic coefficients are typically specified at standard atmospheric conditions. Corrections are applied for actual shooting conditions.
Density Altitude Correction:
BCcorrected = BCstandard × (ρstandard / ρactual)
Where:
- ρstandard = Air density at standard conditions
- ρactual = Air density at actual conditions
Standard Conditions (Army Standard Metro):
- Temperature: 59°F (15°C)
- Pressure: 29.53 inHg (1000 hPa)
- Humidity: 78%
- Altitude: Sea level
Calculated Air Density Ratio: 1.000 (Standard conditions)
Corrected G1 BC: 0.465
4. Drag Model Comparison
Different standard drag models are used for different bullet types:
- G1: Flat-based with 2 caliber tangent ogive (standard model)
- G7: Long, boat-tailed bullet with 10 caliber secant ogive (better for modern long range bullets)
- G5: Shorter boat-tailed bullet, tangent ogive
- G6: Flat-based bullet with secant ogive
For modern long-range bullets, G7 typically provides a more consistent BC across velocity ranges, meaning the BC value changes less as the bullet slows down. This gives more accurate predictions at extended ranges.
For this projectile, the equivalent BCs are:
- G1 BC: 0.465
- G7 BC: 0.238
BC Theory
Key Formulas
Practical Applications
Ballistics Glossary
Understanding Ballistic Coefficient
Ballistic coefficient (BC) is a measure of a bullet's ability to overcome air resistance in flight. It represents the ratio of a bullet's sectional density to its form factor, compared to a standard projectile model.
Key concepts related to ballistic coefficient include:
- Higher BC Values: Indicate more aerodynamic bullets that maintain velocity better, experience less drop, and are less affected by wind.
- Drag Models: Different standard models (G1, G7, etc.) represent different projectile shapes. Modern bullets typically match G7 better than G1.
- Velocity Dependence: BC often changes at different velocities, especially for G1 models. Manufacturers may publish multiple BCs for different velocity ranges.
- Environmental Effects: Air density affects drag, so BC values should be adjusted for temperature, pressure, humidity, and altitude.
Factors Affecting Ballistic Coefficient
- Bullet Shape: Streamlined shapes have higher BCs, with boat tails, secant ogives, and pointed tips improving aerodynamics.
- Sectional Density: Heavier bullets of the same caliber have higher sectional densities and therefore higher BCs.
- Meplat (Tip) Size: Smaller meplats (bullet tips) reduce drag and increase BC.
- Surface Finish: Smoother finishes reduce drag and improve BC.
- Stability: Properly stabilized bullets in flight maintain their intended orientation, preserving their effective BC.
Essential Ballistic Formulas
Sectional Density
SD = W / (D² × 7000)
Where:
- W = Bullet weight in grains
- D = Bullet diameter in inches
- 7000 = Grains per pound
Ballistic Coefficient
BC = SD / i
Where:
- SD = Sectional density
- i = Form factor (relative to standard projectile)
Deceleration Due to Drag
a = -C × ρ × v² × A / (2 × m)
Where:
- a = Deceleration
- C = Drag coefficient
- ρ = Air density
- v = Velocity
- A = Cross-sectional area
- m = Mass
Density Altitude Correction
BCcorrected = BCstandard × (ρstandard / ρactual)
Where:
- ρstandard = Air density at standard conditions
- ρactual = Air density at actual conditions
G7/G1 BC Conversion (Approximation)
BCG7 ≈ BCG1 × 0.512
Note: This is a rough approximation. Actual conversion depends on specific bullet design.
Kinetic Energy
E = 0.5 × m × v²
For bullets (imperial units):
E(ft-lbs) = (W × v² / 450240)
Where:
- W = Bullet weight in grains
- v = Velocity in fps
Wind Drift Approximation
Drift = (W × R² × 1.5) / (BC × v)
Where:
- W = Wind speed (mph)
- R = Range (hundreds of yards)
- BC = Ballistic coefficient
- v = Average velocity (fps/1000)
Note: This is a simplified approximation. Actual drift calculations use step-by-step integration.
Practical Applications of Ballistic Coefficients
Long Range Shooting
+For long range shooting, ballistic coefficient becomes increasingly important:
- Bullet Selection: Higher BC bullets maintain velocity better, resulting in flatter trajectories, less wind drift, and more energy at distance.
- G7 vs G1: For ranges beyond 600 yards, G7 BC is more predictive of actual bullet performance, especially for modern boat-tail bullets.
- Velocity Bands: Using BC values for different velocity ranges improves trajectory predictions, especially beyond 800 yards.
- Transonic Effects: As bullets approach the sound barrier (around 1120 fps), their behavior can change dramatically. Higher BC bullets tend to handle this transition more predictably.
Hunting Applications
+For hunting purposes, ballistic coefficient affects:
- Terminal Performance: Higher BC bullets retain more energy at distance, potentially improving terminal performance.
- Wind Drift: Less wind drift means more precise shot placement, especially in open terrain where wind is a factor.
- Effective Range: Knowing BC helps determine maximum ethical shooting distances, where the bullet still has enough energy and predictable trajectory.
- Bullet Selection Tradeoffs: Some high BC bullets may sacrifice terminal performance for aerodynamics. Balance BC with bullet construction suitable for the game being hunted.
- Point of Impact Shifts: Environmental conditions affect BC, which can shift point of impact. Understanding this helps hunters adjust for different conditions.
Military and Tactical Applications
+In tactical scenarios, BC knowledge provides:
- Engagement Envelope: Defines the range within which the projectile maintains sufficient accuracy and energy.
- Supersonic Range: High BC bullets maintain supersonic velocity longer, extending the range of predictable accuracy.
- Reduced Time of Flight: Higher velocity retention from higher BC bullets means less time to target, reducing the chance for environmental variables to affect the bullet.
- Reduced Signature: Boat-tail, high BC bullets often produce less visible trace and dust signature when fired.
Environmental Adaptations
+Adjusting for environmental effects on BC:
- Altitude Compensation: Higher altitudes mean thinner air and less drag, effectively increasing BC. Trajectory calculations must account for this.
- Temperature Effects: Cold air is denser, increasing drag and effectively decreasing BC. Hot air has the opposite effect.
- Humidity Considerations: Contrary to intuition, humid air is less dense than dry air, slightly increasing effective BC.
- Density Altitude: Combined environmental factors can be expressed as density altitude, which provides a single adjustment factor for BC.
Ballistics Terminology
- Ballistic Coefficient (BC)
- A measure of a bullet's ability to overcome air resistance in flight, compared to a standard projectile.
- Sectional Density (SD)
- The ratio of a bullet's weight to its cross-sectional area, calculated as weight in pounds divided by the square of the diameter in inches.
- Form Factor (i)
- A measure of a bullet's drag relative to a standard projectile model. Lower form factors mean more aerodynamic bullets.
- G1 Drag Model
- The most common reference standard for BCs, based on a flat-based bullet with a 2-caliber tangent ogive nose.
- G7 Drag Model
- A drag model based on a long, boat-tailed bullet with a 10-caliber secant ogive nose, better suited for modern long-range bullets.
- Muzzle Velocity
- The speed of a bullet as it exits the barrel of a firearm, typically measured in feet per second (fps) or meters per second (m/s).
- Transonic Range
- The velocity range where a bullet transitions from supersonic to subsonic speed (approximately 1120-950 fps), often characterized by increased instability.
- Boat Tail
- A tapered rear section of a bullet designed to reduce drag and improve stability in flight.
- Ogive
- The curved front section of a bullet. Tangent ogives have a continuous curve from the bearing surface, while secant ogives have a more aggressive curve for better aerodynamics.
- Meplat
- The flat tip or point of a bullet. Smaller meplats typically improve aerodynamics and BC.
- Spin Drift
- The horizontal deflection of a bullet caused by gyroscopic effects of the spinning bullet interacting with the atmosphere and gravity.
- Coriolis Effect
- The apparent deflection of a bullet's path caused by the Earth's rotation, becoming significant at long ranges.
- Density Altitude
- A measure of air density expressed as an equivalent altitude in standard atmospheric conditions, affecting bullet drag and BC.
- Sight Height
- The vertical distance between the bore center and the line of sight, affecting trajectory calculations.
- Zero Range
- The distance at which the bullet path crosses the line of sight, usually adjusted by sighting-in the firearm.