Do You Really Know How a Compound Bow Works?

Understanding how a compound bow actually works is critical for both beginner and seasoned archers. 

Background

With stone arrow points dating as far back as 61,000 years, it is safe to say the relationship between humans and archery is deeply rooted. For thousands of years archery served more or less as a tool for hunting and war. Archery developed differently around the world with the Mongolian horse bow, Japanese yumi, and English longbow all serving as unique adaptations to the same need.

No matter their differences, all of these bows operate on the same principle. As the string is drawn back, energy is stored in the limbs, which is discharged in the firing of an arrow. The further you draw the bow, the more energy you store. The trouble is that as you draw the bow back, the weight you hold increases. Adding weight increases the tension in your body and makes the shot more difficult to execute. Becoming proficient with a traditional bow takes time, dedication, and lots of arrows.

Historically, archery has operated on the principle of energy stored in the limbs of the bow. Then came along a fellow named Holles Allen. Mr. Allen had an idea that would completely revolutionize archery. His idea was to use a basic pulley system to increase the amount of weight he could draw on his bow. Over time Allen tinkered with his design and eventually secured a patent in 1969 for a device to multiply draw-force. It was at this point in time the compound bow came into existence and changed the archery world forever. Understanding how a compound bow works is important in recognizing how revolutionary the idea was.

How a Compound Bow Works

Today the compound bow is the most popular type of bow in America, hands down. A compound bow is any bow that incorporates cams, cables, and/or a pulley system on the bow. The goal of these components is to decrease the amount of weight the archer holds at full draw, thus making aiming much easier. As mentioned, part of the challenge of traditional archery is to control a steady aim while holding the maximum draw weight.

1. Pulleys

Compound bows nearly eliminate the challenge of drawing a string back on a bow with high draw weight using simple pulley systems. In fact, most compound bows let off around 80% of the labeled draw weight. This percentage is called the "let-off". For example, if I was shooting a compound bow with a 70 pound draw weight and an 80% let-off I would be holding only 14 pounds at full draw. In contrast, if I was shooting a traditional recurve or longbow I’d be holding the full 70 pounds. You can probably guess drawing 14 pounds steadily is much easier than holding 70. Try checking out these compound bow recommendations to compare top models in terms of let-off and maximum draw weight. There's also a useful guide near the bottom of that article on how much draw weight beginner compound users should go for.

2. Cams

Today, most compound bows use specially designed cam pulleys to achieve the benefit of a lower drawing weight at the end of the draw, making it even easier to hold a draw for an extended period. Cams are located at the tip of the limbs and generally have an asymmetrical shape. The shape of the cam is one of the biggest decisions a bow manufacturer must make. Certain cam designs are better for comfort, while others are better at generating speed.

Recurve bows have a linear draw weight curve which means that the bow is increasingly difficult to draw as it is drawn back, with the end of the draw being most difficult. Conversely, cams achieve let-off by being oval shaped, redirecting the peak weight of the draw toward the first few inches of the draw, with decreased drawing difficulty toward the end of the draw.

If you are into physics, engineering, or just like to figure out how things work, check out this website that discusses the ins and outs of cam performance. Archery junkies will certainly find it interesting. What it says for the average archer is that there is no perfect cam out there. When you buy a bow you’ll have to decide what is most important to you and find a cam(s) that fits your requirements.

3. Increased Performance

Not only do these parts make the bow easier to aim, but they also greatly increase the speed and accuracy of your arrow upon release. It’s not uncommon for bows of today to hit speeds of over 300 feet per second. By comparison, most traditional archers generally get their bows shooting around 150-175 feet per second. Increased arrow speeds have great benefits for archers.

First, the increased speed allows the arrow to travel further. This creates a flatter trajectory and simplifies aiming. Faster arrow speeds also increase your odds of successfully harvesting an animal while hunting. Skittish animals like whitetail deer are well-known for their ability to “jump the string” and dodge arrows in flight. Ease of aim and faster shooting arrows are generally seen as the two biggest benefits of compound bows.

In the end compound bows applying a few basic scientific and engineering principles in order to make it a more effective hunting and shooting tool. If you’re still wondering how a compound bow works, you can watch this brief video for good basic visual demonstration. Pay close attention to how the cams roll over right before the shooter hits full draw.  Here is another cool video showing cams working in slow motion.

Conclusion

As an archer who shoots and hunts with both a compound bow and traditional bow, I can personally attest to the advantages a compound bow has. With just a few practice sessions under my belt I can feel comfortable hunting to ranges out to 40 yards with my compound. If I put in more time on the range that distance can stretch out considerably further. The ability to shoot accurately at that distance increases my chances in ways only seasoned bowhunters can really comprehend. With my traditional bow however, even with routine practice sessions, I am generally effective out to about 20 yards. Both bows are fun to shoot and both get you outdoors and learning more about the wonderful world we call home. In the end, if you are looking for a bow that uses some basic engineering to really increase your performance, a compound bow is a great choice.

NEXT: CHOOSING ARROW NOCKS IS MORE IMPORTANT THAN YOU THINK

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