Ballistic Energy

The Physics of Impact: Understanding Ballistic Energy

In the world of shooting and hunting, "Stopping Power" is a debated and controversial term. However, the physics behind it starts with a simple, quantifiable metric: Kinetic Energy (KE).
Measured in foot-pounds (ft-lbs) in the Imperial system or Joules in the Metric system, bullet energy tells us how much work a projectile can do upon impact. This calculator uses the standard ballistic formula to determine KE based on bullet weight and velocity.

The Formula

The standard formula used by ballisticians in the US is:
KE (ft-lbs) = (Mass × Velocity²) / 450,240

Where:
- Mass is the bullet weight in Grains (not grams).
- Velocity is the speed in Feet per Second (fps).
- 450,240 is a conversion constant derived from gravity (32.16 ft/s²) and grains-per-pound (7000).

Velocity vs. Mass

Because velocity is squared in the formula, speed has a much greater impact on energy than weight does.
- Doubling the weight doubles the energy.
- Doubling the velocity quadruples the energy.
This is why a tiny 55-grain bullet from an AR-15 (moving at 3200 fps) can have more kinetic energy than a heavy pistol bullet moving slowly.

Hunting Recommendations (Rule of Thumb)

While shot placement is always king, ethical hunting requires a minimum amount of energy to ensure a clean, humane kill. Common guidelines suggest:

Small Game (Varmints, Rabbits):
- Energy: Less than 300 ft-lbs is usually sufficient.
- Calibers: .22 LR, .17 HMR.

Medium Game (Whitetail Deer, Antelope):
- Energy: 1,000 ft-lbs minimum at the range of impact (not just the muzzle).
- Calibers: .243 Win, .30-30, .308 Win (at longer ranges).

Large Game (Elk, Moose, Black Bear):
- Energy: 1,500 - 2,000 ft-lbs recommended.
- Calibers: .30-06, 7mm Rem Mag, .300 Win Mag.

Dangerous Game (Brown Bear, Buffalo):
- Energy: 2,500 - 3,000+ ft-lbs.
- Calibers: .375 H&H, .45-70 Govt (hot loads).

Energy Decay

Remember that the number calculated here is likely your Muzzle Energy (if you entered muzzle velocity).
Bullets lose velocity rapidly due to air resistance (drag). A bullet that leaves the barrel with 2,500 ft-lbs might only have 1,200 ft-lbs left by the time it travels 400 yards. To be an ethical long-range hunter, you must know your bullet's ballistic coefficient and check a drop chart to ensure you still have sufficient energy at your target distance.