The Perfect Arrow
How to balance speed with kinetic energy.
Arrow selection enables you to make an immediate impact on the way your bow shoots. Basically, there are three shaft categories: lightweight, midweight and heavyweight. For our purposes, a lightweight arrow is one that has a total finished weight of five to six grains for each pound of your bow’s draw force. A midweight arrow weighs six to eight grains per pound of draw force. And a heavyweight arrow weighs more than eight grains per pound of draw force. Each size has strong and weak points; here’s how to find the perfect arrow for your needs.
Penetration vs. Speed
Sometimes it’s worth giving up a little penetration for more speed. For example, a bowhunter who shoots a moderately aggressive cam bow with a 70-pound draw and 30-inch draw length should be getting speeds of 275 to 300 feet per second (fps) with a lightweight arrow, 250 to 275 fps with a midweight arrow and 225 to 250 fps with a heavy arrow. Using the middle of each range as the comparison, the midweight arrow is roughly 10 percent faster than the heavy arrow (for comparison, I used nine grains per pound to represent the heavy arrow), and the lightweight arrow is roughly 20 percent faster than the heavy arrow.
Next, let’s compare the penetration (kinetic energy) of the arrows as they get lighter. By my calculations, changing the shaft weight from 9 grains to 7.5 grains per pound reduces the bow’s efficiency by 3.5 to 5 percent (depending upon the bow). That’s not a huge change. When the shaft weight goes from 9 grains per pound of draw force to 5.5 grains per pound, the bow’s efficiency drops another 5 percent. The lightweight arrow from the same bow would now carry about 10 percent less energy than the heavy arrow. So even with a pretty large swing in arrow weight (245 grains), the shaft loses just 10 percent of its penetration energy.
Speed vs. Noise
A light arrow doesn’t soak up as much of the bow’s energy as a heavy one. As a result, the bow has more energy to dissipate after the arrow is gone, which causes more vibration and bow noise. If a quiet bow is your biggest need, then shoot a heavyweight arrow.
Price vs. Straightness
Most arrows are manufactured in grades. Typically, there is only one difference that separates categories: straightness. Top-grade arrows have straightness tolerances of +/-.001 to +/-.003 inches. Lower-grade arrows have straightness tolerances of +/-.003 to +/-.010 inches. Except at extreme distances, the difference in accuracy is slight. So unless you plan to do a lot of long-range shooting, there’s no reason to spend extra for arrows that are only a few thousandths of an inch straighter.
Diameter vs. Tuning
A small-diameter (carbon) shaft is tougher to tune because you have to move the rest’s arms closer together to support the arrow. Because of this, aluminum arrows with wider-diameter shafts are easier to tune.