Archery Question - Stacking, Wall and Let Off

Q

"Hello!

I see you teach archery and even though I don't live in Toronto I was hoping you might be able to answer a terminology question for me. Thanks in advance for helping me with this!

Anyway, my question relates to stack. Back in the Autumn I was in the backyard with a friend who has been doing archery a lot longer than me and he told me that my compound bow stacks a lot. I didn't want to look stupid at the time so I just sorta nodded and said "Yeah, it does." because stacking a lot sounded like a compliment to me.

However when I tried researching what stack means I came across a lot of references to longbows and shortbows, and nothing about compound bows. So my questions for you are: What is stack? What does it mean when he says my compound bow stacks a lot?

Thanks again for your help!
Michael A."

A

Hey Michael!

Your confusion regarding stack is very understandable, especially since your friend was using the wrong term.

The correct term for them to be using is Wall, sometimes referred to as a High Wall if it is particularly difficult to pull as it gets closed to the Wall. Compounds bows sometimes have a "Forgiving Wall" or a "smooth draw", which means it isn't as difficult to pull as you get closed to the Wall, but often means the bow in question loses a few fps in arrow speed on release. Your compound bow is apparently one of the High Wall / merciless designs, which are made for speed and not draw comfort.

Because compound bows have pulleys they cannot get stack.* (I will explain what stack is in a moment). Instead compound bows get harder and harder to pull back on until they reach what is known as the Wall, and once "over the Wall" you experience the Let Off when the compound bow suddenly becomes a lot easier to pull.

So for example if you have a 50 lb bow with 80% Let Off, the Wall will feel like you are pulling 50 lbs, but once you get past the Wall the left off kicks in and the bow feels like it is only 10 lbs pull.

I also applaud you for trying to research what Stack really means. You are correct, stack relates to longbows and shortbows.

Stack is the angle of the bowstring to the limb tip, which due to physics makes the bow's pull weight feel heavier than it really is. When the bow is relaxed, the string angle on a longbow is very narrow, but as you pull back the string angle widens dramatically. The wider it becomes the more a longbow will stack, making it feel harder than it really is.

Thus Stack and Wall does feel similar when you are pulling back on a bow, hence your friend's confusion of the two terms. I am guessing your friend is into longbows or shortbows, and thus learned of the term but didn't know what Stack actually means.

Shortbows stack more than longbows, due to sharper angle of the tips.

In the case of recurve bows or bows with reflexed or recurved tips, they still stack, but thanks to the recurved shape of the tip the angle of the string to the tip is reduced. Thus recurved bows still stack, but the amount of stack is reduced significantly depending on the bow.

This is why you will often see recurved bows with very dramatically curved limb tips that have been designed in order to maximize the amount of reduction in stack. (See the image further below.)

If you want to learn more about Stack and how it works (on a physics level) I recommend reading The Traditional Bowyer's Bible (Volume One) and read Chapter 3 on "Bow Design and Performance" by Tim Baker.

A Highly Recurved Limb Tip