Formula Used
- Kinetic energy: E = ½ · m · v²
- Exponential velocity decay: v(x) = v₀ · e^(−λx)
- Quadratic drag (simplified): dv/dx = −c·v² ⇒ v(x)=v₀/(1+c·v₀·x)
These models approximate speed loss with distance. Real-world results depend on projectile shape, stability, environment, and measurement uncertainty.
How to Use This Calculator
- Enter bullet mass and muzzle velocity using your preferred units.
- Set maximum distance and step size to control table detail.
- Select a velocity loss model:
- No loss: quick baseline check.
- Exponential: enter a reference velocity at a known distance.
- Quadratic: supply BC and tune the coefficient using real data.
- Click Calculate to view the distance table.
- Use Download CSV or Download PDF to export results.
Example Data Table
Sample inputs: 124 gr, 1150 fps, 950 fps at 100 yd, step 50 yd, max 300 yd.
| Distance (yd) | Velocity (fps) | Energy (J) | Energy (ft-lb) |
|---|---|---|---|
| 0 | 1150.00 | 493.61 | 364.07 |
| 50 | 1045.23 | 407.77 | 300.75 |
| 100 | 950.00 | 336.85 | 248.45 |
| 150 | 863.45 | 278.27 | 205.24 |
| 200 | 784.78 | 229.87 | 169.55 |
| 250 | 713.28 | 189.90 | 140.06 |
| 300 | 648.30 | 156.87 | 115.70 |
Example values are illustrative and will vary by load and conditions.
Energy depends on velocity
At every range, the calculator uses E = ½·m·v², so velocity dominates. If mass stays fixed and speed drops 10%, energy drops about 19%. Example: 124 gr at 1150 fps is about 513 J at the muzzle; 950 fps at 100 yd is about 351 J. This is why small speed errors matter.
Retention across distance
The distance table shows velocity and energy at each step from 0 to your max range. With a 50 yd step to 300 yd, you’ll see seven rows. Tightening to 25 yd doubles the row count and can reveal where energy crosses a chosen limit sooner. Exports keep the same row spacing you set.
Using a reference point
With the exponential model, supplying a measured velocity at a known distance lets the tool solve λ. If v0 = 3200 fps and v100 = 2900 fps, λ becomes about 0.00103 1/m. That single data point often matches chronograph trends better than guessing a decay rate.
Choosing step size
Step size changes readability and export size. A 500 yd run at 100 yd steps yields 6 rows; at 10 yd steps it becomes 51 rows. For quick comparisons between two loads, use larger steps first, then refine around the ranges that matter most to you. Keep steps consistent when comparing load A to load B.
Unit conversions at a glance
You can input mass in grains, grams, kilograms, or pounds, and speed in fps, m/s, km/h, or mph. Useful checks: 1 fps = 0.3048 m/s and 1 J = 0.7376 ft‑lb. If you prefer ft‑lb, the tool reports both units together.
Weather and air density
The quadratic option scales drag using estimated air density from temperature, pressure, and humidity. At 15°C and 1013 hPa, density is near 1.225 kg/m³. Warmer or higher-altitude air lowers density, reducing drag and keeping energy slightly higher at the same distance. Humidity matters slightly.
Reading practical thresholds
Energy numbers become meaningful when tied to a goal. Many shooters watch for 1000 ft‑lb, 500 ft‑lb, or a personal minimum. Use the “Energy drop vs start” column to see percentage loss; a 40% drop means only 60% of muzzle energy remains.
FAQs
What inputs affect energy the most?
Velocity affects energy the most because energy scales with v². A 5% speed change changes energy by roughly 10%. Mass still matters, but smaller mass changes usually have less impact than speed differences.
Which velocity loss model should I pick?
Use Exponential when you have a measured velocity at a known range; it fits a decay rate from real data. Use Quadratic when you want a simple BC and weather adjustment. Use No loss only for quick baselines.
How is energy calculated at each distance?
For every row, the tool converts mass and velocity to SI units and applies E = ½·m·v². The velocity at that distance comes from your selected loss model, then energy is reported in joules and ft‑lb.
How do CSV and PDF exports match the table?
Exports are generated from the same computed rows shown on screen. If you change max distance or step size, the export follows that spacing. This makes it easy to compare two loads using identical distance points.
What step size should I use for hunting ranges?
Start with 25–50 yards or 25–50 meters for typical hunting distances. Use 10-unit steps if you need a precise cutoff point, such as where energy drops below your chosen minimum.
How accurate are the results?
These models are simplified and can differ from a full ballistic solver. Accuracy improves when you use chronograph velocity, a realistic reference point, and consistent conditions. Treat outputs as estimates and verify with measured data when possible.