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Ballistics

Energy Calculations

Foot pounds

It is amazing how many authors write about the subject and have it all wrong. I will give a brief outline on the energy foot pounds calculation theory and calculations.

Any questions can be emailed to me and I will explain further : info@capebuffalo.co.za

Energy

(of motion) - Kinetic energy or force carried by a bullet at that point in its trajectory. In common use and popular shooting literature it is expressed in foot-pounds, one ft/lbs being the amount of force required to lift a one-pound weight one foot above the ground.  Formula: Energy ( in ft/lbs ) equals bullet weight ( in grains ) multiplied by the velocity ( in feet per second ) squared, divided by 450240.  Often wrongly equated with killing power, energy is not a reliable gauge of this, as it does not take into account penetration or bullet performance.

ENERGY UNITS

One foot-pound is the amount of energy expended when a force of one pound acts through a distance of one foot along the direction of the force.

1 foot-pound is equivalent to:

For example - one would calculate the kinetic energy of an 80 kg mass traveling at 18 meters per second (40 mph) as:

Kinetic Energy = .5*80*18*18 = 12,960 joules

Note that the kinetic energy increases with the square of the speed. This means, for example, that an object traveling twice as fast will have four times as much kinetic energy.

Thus, the kinetic energy can be calculated using the formula:

Ek is the kinetic energy in joules , m is the mass in kilograms, and , v is the speed in meters per second.

Ballistics calculation.

To calculate the foot-pound force (ftlbf) of energy for a bullet in English units of measure; given bullet weight in grains and velocity in feet per second, use the following formula.

W = mv  = energy[ftlbf] = weight[grf] (velocity[ft/s]) / (2 32.1739 ft/s 7000 grf/lbf).

Playing with numbers- Energy, Velocity, Weight and Momentum.

The lighter something is, the easier it is to accelerate it to a high speed. By shaving a few grains off a bullet's weight, muzzle velocity can be increased, and this gives a big increase in muzzle energy, since

Energy = x Mass x Velocity2

or

Energy (ftlbs) = [(Velocity (fps))2 x Weight (grains)] 450,240

 

Please refer to reloading manuals at all times, Nosler provides for excellent reading material.

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