Retained Energy

Retained energy is the kinetic energy a bullet still possesses at some point downrange, after air drag has bled off part of the speed it left the muzzle with. Because energy scales with the square of velocity, it falls faster than velocity does, which is why a round that hits hard up close can be marginal at distance. Shooters usually express it in foot-pounds and read it straight off a ballistic table for the range in question.

The figure matters most for terminal performance, since many hunting standards set a minimum energy for a clean, ethical kill on a given animal. A bullet’s retained energy is simply derived from its retained velocity and weight, so a high ballistic coefficient that preserves speed also preserves energy. Comparing retained energy against muzzle energy shows how much a load has given up by the time it reaches the target.