Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm.
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.
Ek = 1/2 x m x v²
where
v is the velocity of the bullet
m is the mass of the bullet.
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:
Ek = 1/2 x (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
E is the energy in foot pounds.