Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is often used as a rough indication of the destructive potential of a given firearm or load. The heavier the bullet and especially the faster it moves, the higher its muzzle energy and the more damage it will do.
The general formula for the kinetic energy is
:''v'' is the velocity of the bullet
:''m'' is the mass of the bullet.
A subsonic variant of ammunition that would otherwise be supersonic has its velocity limited to less than the speed of sound, i.e. ''v'' is fixed at around . For ammunition with this limitation the muzzle energy is a function only of the bullet mass ''m''.
==Calculating muzzle energy==
*In the SI system the above ''Ek'' will be in unit joule if the mass, ''m'', is in kilogram, and the speed, ''v'', is in metre per second.
*In United States engineering units, particular care must be taken to ensure that consistent units are used.
*Mass, ''m'', is usually given in grains and the speed, ''v'', in feet per second but kinetic energy, ''Ek'', is typically given in foot-pound force (abbreviated ft-lbf). Most sporting arms publications within the United States report muzzle energies in foot-pound force. If ''m'' is specified in grains and ''v'' in feet per second, the following formula can be used, which gives the energy in foot-pound force:
*When publishing kinetic energy tables for small arms ammunition, an acceleration due to gravity of 32.163 ft/s2 rather than the standard of 32.1739 ft/s2 is used. The formula therefore becomes
The bullet energy, remaining energy, down range energy, and impact energy of a projectile may also be calculated using the above formulas.
The first of the two US formulas can be simplified in conformance with US practice to:
E = (M x V²) ÷ K
where K = 450,435 and is derived from (2 x 32.1739 x 7000),
M is the weight of the projectile, in grains,
V is the velocity in feet per second and
E is the energy in foot pounds.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』