Muzzle energy

The general formula for the kinetic energy is

${\displaystyle E_{\mathrm {k} }={\frac {1}{2}}mv^{2}}$

where

v is the velocity of the bullet

m is the mass of the bullet.

Although both mass and velocity contribute to the muzzle energy, the muzzle energy is proportional to the mass while proportional to the square of the velocity. The velocity of the bullet is a more important determinant of muzzle energy. For a constant velocity, if the mass is doubled, the energy is doubled; however, for a constant mass, if the velocity is doubled, the muzzle energy increases four times. In the SI system the above E_k will be in unit joule if the mass, m, is in kilogram, and the speed, v, is in metre per second.[1]

Muzzle energy is dependent upon the factors previously listed, and velocity is highly variable depending upon the length of the barrel a projectile is fired from.[2] Also the muzzle energy is only an upper limit for how much energy is transmitted to the target, and the effects of a ballistic trauma depend on several other factors as well. While the above list mentions some averages, there is wide variation in commercial ammunition. A 180-grain (12 g) bullet fired from .357 magnum handgun can achieve a muzzle energy of 580 foot-pounds force (790 J). A 110-grain (7.1 g) bullet fired from the same gun might only achieve 400 foot-pounds force (540 J) of muzzle energy, depending upon the manufacture of the cartridge. Some .45 Colt ammunition can produce 1,200 foot-pounds force (1,600 J) of muzzle energy, far in excess of the average listed above.

Some jurisdictions stipulate minimum muzzle energies for hunting. For example, in Denmark rifle ammunition used for hunting the largest types of game there such as red deer must have a kinetic energy E₁₀₀ (i.e.: at 100m range) of at least 2700 J and a bullet mass of at least 9 g or alternatively an E₁₀₀ of at least 2000 J and a bullet mass of at least 10 g.[3] Namibia specifies three levels of minimum muzzle energy for hunting, 1350 J for game such as springbok, 2700 J for game such as hartebeest and 5400 J for big game, together with a minimum caliber of 7 mm.[4]

In Germany airsoft guns with a muzzle energy of no more than 0.5 J are exempt from the gun law,[5] while air guns with a muzzle energy of no more than 7.5 J may be acquired without a firearms license.[6]

Mainland China uses a 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 gram 6mm pellet have a muzzle velocity over 250 ft/s (76 m/s), which translates to more than 0.58 J (0.43 ft⋅lbf) of muzzle energy, or 2.0536 J/cm² of "ratio energy". The subsequent heavy-handed crackdowns by local law enforcement led to many seizures, arrests and prosecutions of individual owners for "trafficking and possession of illegal weapons" over the years.

• Free recoil
• Muzzle velocity
• Power factor (shooting sports)

• Edward F. Obert, Thermodynamics, McGraw-Hill Book Co., 1948.
• Mc Graw-Hill encyclopedia of Science and Technology, volume ebe-eye and ice-lev, 9th Edition, Mc Graw-Hill, 2002.