While speed may be a highly considered factor when purchasing a bow or crossbow, kinetic energy is the real factor that an archer should consider. Whether you are bowhunting or just target shooting, once you understand kinetic energy, you will be better able to pick the right arrows or bolts and even broadheads for your archery rig.
The measurable “power” of your bow or crossbow is known as its total kinetic energy output. The equation that determines what your kinetic energy is can be factored with two simple variables: the speed of an arrow and the total mass of the arrow. Many bowhunters are only concerned with the speed of a bow or crossbow but the other side of the equation, arrow mass, must be a serious consideration so you have a properly matched arrow to the speed of your bow. For example, if I had 400 grain arrow shooting out of a 250 fps (feet per second) bow, then my kinetic energy would be around 55 ft-lbs. There are many archery calculators online that can help you determine your total kinetic energy output.
The main thing to keep in your mind is that 55 ft-lbs of kinetic energy is the “sweet spot” for most bowhunting done in North America. If you are after African game species on some exotic safari or hunting Moose, Elk, Bear, or other larger game consider around 65 ft-lbs of kinetic energy to be adequate. If you are after small game like small predators or rabbits, consider around 25-40 ft-lbs of kinetic energy. In other words, the larger the game species, the more kinetic energy you will need to make a clean and ethical harvest.
Kinetic energy is also a serious consideration if you are using mechanical broadheads. What you want to ensure is that you have enough kinetic energy to open a broadhead upon reaching its target of hair, hide, muscle and sometimes even bone to ensure proper penetration of the arrow or bolt. If you shoot a lighter poundage bow, I recommend a smaller blade diameter. I personally shoot a 30” draw length and 62 pound draw weight in my compound archery rig which gives me the ability to shoot a 2” 3-blade mechanical broadhead with good penetration due to the kinetic energy of my set up.
With this all being said, keep in mind that bowhunting is a challenging sport and that is why many of us pursue it. There are many variable factors that can make your hunt successful in the “real world” of hunting. If you ensure you shoot an arrow or bolt matched for your archery rig combined with practice and knowing your equipment well, you will increase your chances of a successful harvest time after time again. May your blood trails be short and your hunting successes be countless.