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What is Muzzle Energy?

Muzzle energy is the kinetic energy of a pellet or bb as it is expelled from the muzzle of a air gun. Measured and indicated by Foot-Pounds of Energy or FPE (or Joules internationally), muzzle energy tends to be a more accurate representation of the power of an air gun. Most manufacturers will state muzzle velocity in feet per second (or FPS) in the product specifications, and is even used throughout the products on our website, but there are problems with simply stating velocity.

The first problem is airgun hunting. Faster velocities donít always mean more knock down power. A light alloy pellet traveling at high velocities wonít have the same knockdown power as a heavier pellet traveling at lower velocities. Because of this, experienced air gunners are becoming more aware of muzzle energy when choosing an air gun for hunting pests or varmints. You can learn more about FPS vs FPE in our exclusive article: Faster Isn't Always Better.

Secondly, there are many countries that restrict air gun ownership based on muzzle energy, not velocity. This makes it complicated, often difficult, for shoppers and merchants alike.

Below are two calculators that will help you calculate Muzzle Energy (FPE) and Muzzle Velocity (FPS):

FPE Calculator
Pellet Weight:  Grain
Velocity:  FPS

Foot-Pounds of Energy (FPE)


Joules
FPS Calculator
Energy:  FPE
Pellet Weight:  Grain

Feet Per Second (FPS)


To calculate muzzle energy, you would take the pellet weight (in grains) and multiply that by the pellet velocity squared. That number is then divided by two times the acceleration of gravity by the total number of grains in a pound. Here is what the formula would look like:

FPE = Pellet Weight * FPS2/(2 * Acceleration of Gravity) * Total Grains


The second part of the formula contains several constants. The first constant, acceleration of gravity, is the standard acceleration due to free fall of 32.16fps. The second constant, Total Grains, is 7,000 which is the total number of grains in a pound.

If we take these constants and add some example numbers into our formula, 8 grains for pellet weight and 1000 fps for velocity:

FPE = 8 * 10002/(2 * 32.16) * 7000


FPE = 8 * 1000000/64.32 * 7000


FPE = 17.77


In this example, the muzzle energy for this particular air gun and pellet is 17.77 fpe, or joules. For more information on the difference between FPE and FPS, take a look at our exclusive article: Faster Isn't Always Better: Why Muzzle Energy Is An Important Factor In Air Rifle Hunting.
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