Muzzle energy

Without consideration of factors such as aerodynamics and gravity for the sake of comparison, muzzle energy is used as a rough indication of the destructive potential of a given firearm or cartridge.

In the SI system the above Ek will be in unit joules if the mass, m, is in kilograms, and the speed, v, is in metres per second.

A 110 gr (7.1 g) bullet fired from the same gun might only achieve 400 ft⋅lbf (540 J) of muzzle energy, depending upon the manufacturer of the cartridge.

Firearms regulation in the United Kingdom is a complicated example, but is demarked by muzzle energy as well as barrel length and ammunition diameter.

[6] Mainland China uses a varied concept of "muzzle ratio kinetic energy" (Chinese: 枪口比动能), which is the quotient (ratio) of the muzzle energy divided by the bore cross sectional area, to distinguish genuine guns from "imitation" replicas like toy guns.

The Ministry of Public Security unilaterally introduced the concept in 2008 leading up to the Beijing Olympic Games, dictating that anything over 1.8 J/cm2 to be defined as real firearms.

This caused many existing toy gun products on the Chinese market (particularly airsoft) to become illegal overnight, as almost all airsoft guns shooting a standard 0.20 g (3.1 gr) 6 mm (0.24 in) pellet have a muzzle velocity over 76 m/s (250 ft/s), which translates to more than 0.58 J (0.43 ft⋅lbf) of muzzle energy, or 2.0536 J/cm2 of "ratio energy".