Foot pounds are a commonly used unit of energy when discussing small projectiles such as bullets, pellets, arrows and bolts. I believe the author's use of "foot

Foot pounds are a commonly used unit of energy when discussing small projectiles such as bullets, pellets, arrows and bolts. I believe the author's use of "foot pounds per square inch" was an error. WolframAlpha calculates the energy of a 40 grain bullet at 1550 feet per second to be 213.3 foot pounds, not 324. Winchester claims that a 40 grain .22 magnum bullet from a rifle-length barrel exits the muzzle at 1910 feet per second and has 324 foot pounds of kinetic energy. WolframAlpha agrees.