What is FPS and what is FPE?

FPS is feet per second, which measures velocity at the muzzle.

FPE is foot-pounds of energy, which measures the actual kinetic energy the projectile carries. The formula is FPE = (weight in grains x velocity squared) / 450240. FPE matters more than raw FPS because a heavy pellet at moderate velocity often produces more energy and penetrates better than a light pellet shot fast. Manufacturers love to advertise high FPS using the lightest alloy pellets, which is misleading for hunting purposes.