Muzzle Energy
The kinetic energy a bullet carries as it leaves the muzzle, computed from its weight and its muzzle velocity.
Muzzle energy is the kinetic-energy of the bullet at the instant it exits the bore, derived from the projectile’s bullet-weight and its muzzle-velocity. Because the energy scales with the square of velocity, speed contributes far more than mass, which is why a small increase in velocity moves the energy figure substantially. The result is conventionally expressed in foot-pounds in the United States.
Muzzle energy is the starting point of an energy budget that only decreases downrange as drag bleeds off speed, so the number at the muzzle is always the maximum the load will deliver. Past the muzzle the relevant quantity becomes retained-energy, the lower figure the bullet still carries at a given distance, which is what governs terminal effect on target.