When you branch into the world of hunting with air rifles, the term most frequently used is foot-pounds of energy. In this video from American Airgunner , Jim Chapman, Tom Gaylord, Rossi Morreale, and Rick Eutsler discuss the term and what it means.

Key Takeaways

1. One take away from this video is the understanding that buying an air rifle based on the Feet-Per-Second is not how you should make your purchase since the weight of the bullets for hunting you shoot will change that during the shot.
2. Everyone is used to looking at feet per second. Speed does not tell us what it will do on game animals. It is a part of the calculation. 
3. We think in terms of speed but need to look at what type of energy the pellet produces it produces when hitting a target. When hunting for big or small game, we need to look at the pellet’s weight multiplied by the Velocity Squared, divided by 450395. Conventional wisdom has held that 1,000lbs foot-pounds of energy are required to kill a deer. However, users of the Umarex Hammer are easily killing big game as large as cape buffalo with a 550-grain bullet shooting 790 fps producing 705 foot-pounds of energy. 
4. Tom Gaylord wrote in an article for Pyramid Air saying, “A .45-caliber lead bullet generating 250 foot-pounds of energy will kill a medium-sized animal such as a whitetail deer just as dead in the same amount of time as a .45-caliber lead bullet that generates 1,500 foot-pounds of energy. That’s because most of the more powerful bullet’s energy is not expended in the animal — it slips right through and keeps on going! Most of the energy is excess to your needs.” 
5. The energy of your bullet or pellet, not the speed, is what you rely upon in airgun hunting. Penetration and blood loss is what you must consider when preparing for a big game hunt. 

This great video from American Airgunner is a fantastic breakdown directly from the experts on foot-pounds of energy in airgun hunting.