Bowhunting and Kinetic Energy

You bring your bow out into the yard for some target practice. You're shooting at the bulls-eye and putting 3 arrows inside of a 3 inch circle. Your speed is phenomenal. It's like as soon as you pull the trigger the bow has passed 40 yards and placed itself into the target in the same millisecond. You can't believe the speed you're getting, but there is one problem, the arrow is not penetrating deep enough into the Styrofoam. Heck, your arrow could perhaps bounce off a deer. What seems to be the problem though? The chronograph recorded you at a blistering 297fps. I'll tell you what the problem is, lack of kinetic energy.

Everyone is so caught up in the speed game. People are overbowing their bows, pulling their draw length back 1-3 inches too long for them, using arrows so light they might as well dry fire their bows. What they do not see, is that kinetic energy is what kills deer, not speed. Yeah, so you're shooting nearly 300fps with a full set up, but do you really think that means that a deer still can't jump your string? Speed is important, very important, but not as important as the kinetic energy you're shooting.

So what is "kinetic energy?" Kinetic energy basically means the amount of penetration your bow is going to produce at a certain arrow velocity. To measure the amount of kinetic energy your bow is shooting, the formula is: speed * speed * arrow weight / 450240. You can see the importance of speed in the formula, but the most under looked aspect in the formula is the arrow weight. IBO recommends you shoot 5 grains of arrow weight for every pound of draw weight, but that is for maximum speed standards and is basically dry firing your bow. You need about 6-8 grains of arrow weight for every pound of draw weight. Yes, this will slow you down a slight bit, about 1fps worth for every 3 grains of arrow weight, but you will gain what is really important: kinetic energy.

There are calculators on the computer that will help you determine your speed and kinetic energy if you do not have access to a chronograph, but the easiest method to determine at home is simply know the IBO standards, which is 30 inches of draw length, 70 pounds of draw weight, and a 350 grain arrow. If your bow does not reach a 30 inch draw or 70 pounds of weight, then use the maximum weight/length your bow comes in and times the draw weight by 5 to determine the total grain arrow used. So if you're using a bow that has an IBO of 335 fps: subtract 10 fps for every inch of draw length lost, subtract 2 fps for every lb of draw weight lost, subtract 1fps for every 3 grains of arrow weight lost, and that should tell your your speed, give or take 5 fps or so.

In example, your bow has an IBO of 335fps, so if your bow is set on 28 inches of draw length, 70 pounds of draw weight, and you're shooting a 427 grain arrow, then your approximate speed is 286 fps and your total kinetic energy is 78 ft/pds of kinetic energy.

Remember to pay a little bit of attention to the kinetic energy your bow is shooting. Don't get so caught up in speed that you lose sight of everything else. Speed is very important, but the total kinetic energy is what you want to look for. Find you a fast bow, put a somewhat heavy arrow on it, and then see how far that arrow penetrates into the target.

By Will E Riggs