I hadn't realized some countries had muzzle energy laws. Some seem pretty stupid.
Many parts of the world use muzzle energy to classify guns into categories that require different categories of licence. In general guns that have the potential to be more dangerous have tighter controls, while those of minimal energy, such as small air pistols or air rifles, require little more than user registration, or in some countries have no restrictions at all.
Overview of gun laws by nation indicates the various approaches taken.
Firearms regulation in the United Kingdom is a complicated example, but is demarked by muzzle energy as well as barrel length and ammunition diameter.
Some jurisdictions also stipulate
minimum muzzle energies for safe 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 100 m 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 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 gram
6 mm 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/cm
2 of "ratio energy". For comparison a
standard baseball changeup thrown at 75 mph (34 m/s) has 1.951 J/cm
2 of "ratio energy" which also exceeds the 1.8 J/cm
2 level of a real firearm while a
fastball can reach over 3.5 J/cm
2 or nearly double the level of a real firearm. The subsequent 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 for weapons that were previously permitted.