Archery is a sport that’s based on physical science. If it weren’t for an understanding of physics (the study of matter and energy) and kinetic energy (the study of energy associated with motion and material bodies), we as hunters might still be throwing flint-tipped spears.
Ironically, it’s tradition not scientific fact that guides many of the decisions bow hunters take to the field with them. A polarized group, most bow hunters fall into a traditional following that favors heavy and slow-moving arrows or a growing number of speed seekers who are in favor of lighter arrows moving at maximum speeds.
Regardless of which group you fit into, remember that arrow speed in and of itself has a dramatic effect on trajectory, penetration, and down-range accuracy. Despite traditionalists who view bow hunting as a 20-yard sport, the move inside the archery industry is towards high-energy cams, carbon bow limbs, overdraws, fast-flight strings, lighter arrows, and anything else that might provide a few extra feet per second (fps) of arrow speed and a few extra feet of effective hunting range.
If you’ve been feeling a need for speed, read on and learn how to select speed bows or turn the heat up on your bow a couple notches.
Trajectory, Accuracy, Penetration
Trajectory, penetration, and accuracy are three of the most important variables a bow hunter faces. If any one of these variables is out of proportion or lacking, success is doomed from the start.
Arrow speed has the most profound effect on trajectory. Objects hurled through the air all suffer from the negative effects of gravity pulling the object towards Earth. The slower an object moves, the faster gravity affects the flight of the object.
The path of a moving object can be described as an arc or what is commonly referred to as trajectory. When a pitcher hurls a baseball from the mound, the ball covers the distance quickly and crosses the plate without noticeable trajectory. However, in order to throw out a runner going home, an outfielder must throw the ball high into the sky to compensate for the arc or trajectory of the ball in flight. If the outfitter throws the ball directly at the target, the ball will hit the ground long before it reaches home plate.
The trajectory problems associated with moving objects is solved in baseball by hitting the cut-off man. It’s generally accepted that two short throws can be made more accurately than one long throw. In archery there are no cut-off men. In order to achieve consistent accuracy at distances beyond 25 yards, arrow speed must be sizzling and trajectory as flat as possible.
How fast is fast? Arrow speeds these days frequently exceed 300 fps. Tournament IBO shooters are the driving force behind increased arrow speeds. These shooters are required to hit 3-D targets from unmarked distances. Misjudging a target by as little as five yards is enough to cause a low score or a complete miss. With cash, prizes, and fame at stake, it’s easy to see why competitive 3-D shooters are always striving for increased arrow speeds and the improved accuracy that’s possible with a flat- shooting bow.
Blazing IBO speeds are achieved by shooting arrows that weigh 5 grains per pound of draw weight or approximately 300-350 grains. Compared to a typical hunting arrow that weights 450-540 grains, it becomes obvious why bows set up for IBO shooting are so fast.
The blazing speed of an IBO bow isn’t necessary when shooting at targets from 10-20 yards. Even the slowest hunting bows have a modest trajectory when the targets are at 10, 15, or 20 yards. If the targets are moved out to 25, 30, 35, and 40 yards, however, note how progressively difficult it becomes to score consistently with a slow-moving arrow.
With these points made, the picture becomes clear why shooting accuracy and speed relates directly to trajectory. Still, the question is often raised, can the average hunter shoot accurately at ranges out to 40 yards? The answer is a resounding yes, assuming the hunter takes the time to practice and develop the required shooting skills. Hunters who aren’t willing to practice frequently, are frankly better off shooting only at animals within 25 yards.
As with any sport, you get back what you’re willing to put forth. Developing shooting skills at targets from 25-40 yards requires a commitment on the hunter’s part to practice diligently and learn to estimate target distances accurately. The best way to master these skills is to practice shooting at IBO courses. Shooting at life-like targets and at unmarked distances is the only practice that comes close to actual in-the-field experience.
A third benefit of arrow speed is penetration. The faster an arrow moves, the deeper it is likely to penetrate game. Penetration is also influenced by other factors such as arrow weight, broadhead sharpness, and shaft stiffness. All factors being equal, a fast-moving arrow penetrates better than a slow-moving one.
The extra arrow penetration provided by fast bows is a real advantage when hunting at the extremes. Large animals taken at maximum ranges clearly call for all the penetration an archer can muster.
Last year a caribou hunt in northern Labrador proved to me again that you can never have too much penetration. A large animal, an adult caribou bull is roughly twice the size of a typical whitetail buck. When the bull I carefully stalked presented a now-or-never 40-yard shot, I was confident I could hit the animal in the vitals.
My bow a Mountaineer Ultra Cam was chronographed at 260 fps with 30-inch 2314 XX78 arrows. Tipped with a 80-grain broadhead, my arrow weighed approximately 430 grains.
When my arrow zeroed the bull square in the chest, the impact shattered a rib bone and glanced off another rib before punching through the opposite side. The arrow came to a rest with just the fluorescent green nock showing at the point of impact.
Had the arrow been a little slower and the broadhead not penetrated through the skin on the opposite side, I could have been left with a tough trailing job. As it turned out, the blood trail was steady, and I easily recovered and tagged a dandy double-shovel caribou bull.
Selecting Speed Bows
The shelves of archery pro shops are full of high-quality speed bows. A hunter interested in achieving above-average speed should begin his or her search at bows equipped with an energy wheel or a hard cam.
Energy wheels and cams are progressively out of round as compared to a round-wheel bow. When the bow is drawn and released, the kinetic energy developed from energy wheels or more aggressive cams slings the arrow out of the bow.
Round-wheel bows simply don’t generate enough kinetic energy to qualify as true speed bows unless they are equipped with an overdraw system. The addition of an overdraw can add 20 or more fps of speed to a round-wheel bow. More on overdraws later.
Speed is a wonderful thing in bow hunting, but simply choosing a bow by the manufacturers published speed ratings can be a risky gamble. Unfortunately, some manufacturers play the speed game by rating their bows using IBO requirements instead of AMO standards.
AMO standards are very rigid and require all bows to be tested with a 60-pound peak draw weight, 30-inch draw length, and 540-grain arrow (9 grains per pound). In IBO ratings there are no peak draw weight restrictions. Some manufacturers test their bows at 60 pounds and others at 70 pounds, making it difficult for the consumer to get an accurate assessment of bow speed when comparing models and brands.
Any bow that exceeds 240 fps AMO rating is likely to produce arrow speeds well above 300 fps with IBO ratings (5 grains per pound). The average hunter shooting a 400- to 500-grain arrow is likely to enjoy speeds that range from 250-280 fps. This compromise of AMO and IBO speeds represents an excellent speed range for a hunting bow.