How Does a Compound Bow Work? – Beginner’s Guide

| Last Updated August 7, 2021

A compound bow works like any other type of bow in that you draw an arrow back on the bowstring and rely on the tension created during the draw to shoot the arrow towards a target when you release the bowstring.

However, compound bows are more complex and comprise many moving parts that make it easier for the shooter to launch the arrow. The main advantage of a compound bow is that it significantly reduces the amount of tension built up during the draw.

While this is a simple way to look at it, there is much more to how a compound bow works. Be sure to read through the article to discover in greater depth the dynamics and functionality of compound bows.

Understanding Parts of a Compound Bow

For a beginner, it's important to learn the different parts of a compound bow before you even try to shoot an arrow with it. A good understanding of each part will make it easier to shoot since you already know what each part is for and how it functions.

Limbs

The limbs hold and spread out the tension or energy created when you draw the bowstring. A compound bow has both upper and lower limbs.

Bowstring

The bowstring launches the arrow towards the target once released from the full draw position.

Cams

Compound bow cams are wheel-like mechanisms at the tip of the limbs that help reduce the bow draw weight when you pull back the bowstring to full draw, the farthest possible stretch point.

Cams may either be single cams, hybrid cams, binary cams, or double cams. 

Riser

The riser is a compound bow's central section that carries other components such as the limbs, the stabilizer, the arrow rest, the sight, the grip, and a bow-mounted quiver.

Cables

The cables connect the upper and lower cam. They run 'parallel' to the bowstring between the limbs.

Photo credit: hunter-ed.com

Terms to Know When Dealing with a Compound Bow

The many terminologies used around compound bows because of their complexity owing to the many interdependent parts and their working mechanism might scare you away as a beginner. 

However, once you have the basics, it's easy to grasp each of the concepts. The major terms used around compound bows include but aren't limited to the ones discussed below. 

  • Draw Weight: The force required to pull back the bowstring to the full draw position is called the draw weight and is measured in pounds.

  • Draw Length: The draw length of a compound bow is the furthest distance to which you can draw back the bowstring as controlled or limited by the bow's mechanical systems. 

The easiest way to determine your draw length is to divide your arm span length (fingertip to fingertip) by 2.5. 

  • Brace Height: The distance between the bow grip's throat or pivot point (deepest section of the bow grip) and the bowstring in its resting position is called the brace height. It's technically the 'position' from which the string starts when you start pulling towards the full draw. 

A bow with a short brace height creates more arrow speed but is less forgiving, while one with a longer height has slower arrow speeds and is more forgiving. A compound bow's brace height depends on the manufacturer's settings on the bow. 

  • Axis: The bow sight in a compound bow has three axes. Each axis is an imaginary line that helps you attain higher levels of accuracy with your bow. 

One axis runs parallel to ground level and left-right in front of the archer. The other axis runs through the center of the scope and is usually held as the most crucial of the three. 

The last axis runs through the sight's center, parallel to the archer's body. It is useful when you are shooting downhill or uphill. 

  • Pulleys: The pulley system in a compound bow relies on the cams to reduce the draw weight by about 80%, making holding the bow at full draw easier on the archer during the aim.
  • Flex: When you back the bowstring of a compound bow, the limbs flex and store the bow's energy as the draw weight, which is released when you let go of the bowstring to launch the arrow.

  • Let-off: The amount of bow draw weight the pulley system takes out when you pull to full draw is called the let-off. For example, a 60-pound draw weight bow requires just 12 pounds to pull the bowstring to full draw.

  • Potential Energy: An object's potential energy is its stored energy relative to its position. In a compound bow, an arrow attached to the bowstring in the full draw position has potential energy that converts into kinetic energy once you release the bowstring to shoot.

  • Kinetic Energy: An object in motion has kinetic energy. A shot arrow has kinetic energy as it travels towards the target. The higher the kinetic energy, the higher the speed of the arrow, and the more accurate and effective it becomes. 
  • How a Compound Bows Works

    A compound relies on its system's mechanical advantage to shoot arrows off the bowstring. As seen earlier, the pulley system is a central part of the bow's shooting mechanism. Here's a simple breakdown of how a compound bow works.

    Loading the Arrow

    To use a bow to shoot, you start by loading the arrow on the arrow rest. If your bow doesn't have a rest on it, you load the arrow just like you would in other simpler types of bows such as recurves and longbows.

    Drawing with the Help of the Pulleys

    Once the arrow is armed, you pull back the bowstring through to the full draw. The pulleys come in handy at this point to ease the pressure on your drawing hand, with the draw weight growing lesser and lesser until you reach the full draw length.

    During drawing, the cables move and spread out the energy onto the limbs, which in turn compress - just like a spring does.

    Storing Energy in the Limbs

    The limbs flex during the draw, and the tension remains in them, ready for when you let go of the bowstring to launch the arrow towards the target. 

    At this point, before you fire the arrow, the draw weight is at its peak. However, the let-off makes you only experience a fraction of the weight or tension because of the mechanical advantage of the pulley system.

    Energy Transfer to the Arrow

    At full draw, the arrow has the highest potential energy, which is converted into kinetic energy once you let go of the bowstring. During the release, the limbs relax, and the energy stored in them is transferred to the arrow to propel it towards your target.

    After the shot, the entire system goes back to normal. Each moving part assumes its usual resting position until you arm another arrow to restart the shooting cycle.

    Knowing the Different Cam Configurations

    There are several compound bow cam configurations you can try during archery or bowhunting. Here are the different configurations at your disposal. 

    Single Cam Mechanism

    The single cam system is the most straightforward configuration. It consists of an idler wheel at the top edge of the upper limb and a workhorse cam on the lower limb.

    The idler wheel is for unrolling the bowstring as you pull toward the full draw, while the workhorse bottom cam controls the cable and corrects its downward motion. 

    The single cam configuration is the best bet for beginners because of its simplicity and exceptionally quiet arrow shots. However, it doesn't have as much energy released to the arrow as other configurations. 

    Photo credit: bowhunting.com

    Twin Cam Configuration

    The twin cam system is also called the two cam configuration. The two cams in this setup are put to work simultaneously to produce faster and more accurate shots. 

    However, the twin cam configuration is noisier and harder to maintain since the two cams must be in sync for you to attain the correct arrow flight. 

    Binary Cam Configuration

    The binary cam system offers better and easier synchronization than the twin cam configuration. The cams in this setup are linked together to produce even more accurate shots and shooting consistency.

    Hybrid Cam System

    In a hybrid cam system, the cam in the upper limb helps stabilize the power from the lower limb cam to produce a better, well-balanced shot. The two cams are linked together as in the binary system. 

    The hybrid cam configuration is preferred by archery or bowhunting experts because they offer the best of both worlds of speed and ease of pulling by combining the techniques of single cams (easy pulling) and twin cams (speed).

    Photo credit: hunthacks.com

    Conclusion

    As a beginner, knowing how a compound bow works calls for carefully examining its components and understanding the various terminologies used around compound bows. 

    A compound bow's main functionality point is its pulley system for the reduced draw weight effect and the energy transfer from the string, limbs, and finally, setup of the arrow itself. 

    However, you shouldn't get too hung up on the details and forget to do the main thing you ought to - firing some arrows for practice. It is the practice rather than studying the working mechanism that gets your foot in the door in successful archery and bowhunting.



    My name is Jeff and I have been hunting and fishing for over 40 years. I am an avid archery lover, bass fisherman, and all-around outdoorsman. Currently, I'm obsessed with elk hunting but I'm sure I'll move onto a different favorite soon. You gotta love hunting for that reason :) If you have any questions, or just want chat about your latest hunting score or big catch, you can reach me at admin@biggamelogic.com. Read more about Big Game Logic.