Properly measuring arrow length is important for several reasons.
- The length of an arrow effects the DYNAMIC SPINE of an arrow. Does your 42 pound arrow actually fly like a 45 pound arrow? Do you know?
- The length of an arrow is important because it is used in the FOC equation to determine the balance point of an arrow. Further, does the balance point of this arrow match the balance points of the rest of the arrows in your quiver?
- The overall length of an arrow is NOT the functional length of an arrow. What happens if the arrows you ordered are too short for your bow? Now THAT is an expensive set of arrows indeed!
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Once we know the exact length of the functional part of the arrow, NOT THE OVER ALL LENGTH of the arrow, we can simply calculate how far the balance point of an arrow is forward of the center (commonly referred to as F O C).
- 20.875 inches – 16 inches = 4.875
- 4.875 ÷ 32 = 0.15234375
- .1523 X 100 = 15.23
The balance point of this arrow is just about 15.25% FORWARD OF THE CENTER OF THE ARROW (F O C).
Arrow length is one of 4 major considerations in manipulating bamboo arrows to group tightly enough to start splitting them. This balancing of these four priorities is what I call “The Arrow Maker’s Conundrum”.
Balance point and length are a function of each other, and thus have to be considered jointly. For instance, If this arrow were shortened by just 1 inch, the balance point will shift as well as the center of the arrow. In this case, if the balance point of the arrow is now 20.375, but the arrow is now 31 inches long, the new FOC becomes very nearly 15.75%.
Imagine adding a heavier head to this shortened arrow. This will push the FOC up even more. To have a high FOC is not necessarily good or bad. The same is true for a low FOC. I personally find that arrows above 17% and those below 13% FOC do not group as tightly as those that are in the 15% – 16% FOC range for my arrows shot from my bow. Possibly your experience may be different.
Lastly, when you buy a set of arrow and the FOC values vary beyond 2% within the group, there may be a problem…DEPENDING. Depending on whether the spines and weights are closely aligned or not. I match the arrows in my quiver to be within 1 pound of static spine within all 12 arrows. I also match them to weigh within 20 grains from the heaviest arrow to the lightest arrow within the set of 12 arrows. Heavier arrows fly “stiffer” than lighter arrows. The dynamic spine is stronger. AS AN ARROW MAKER, MY TWO GOALS ARE NOW…AND ALWAYS WILL BE TO MAKE AN EXTREMELY TOUGH SET OF ARROWS WHICH WILL GROUP INTO A TEACUP AT 20 YARDS BECAUSE THEY MATCH AND ARE PREDICTABLE IN FLIGHT.
If I do this, a set of matching arrows with a 13% FOC is just as dependable as a set of arrows with a 16% FOC…FOR GROUPING TIGHTLY. However you may have other priorities in mind. I can make them any way you want, but just so you know…they will ALWAYS be within 1% – 2% FOC if I make them unless you request otherwise.
IN MY OPINION, IT IS NOT VERY IMPORTANT THAT THE ARROWS MATCH EXACTLY BY LENGTH. IT IS CRITICAL THAT THEY GROUP TIGHTLY!
It isn’t too obvious, but if you study this photo, you will see that some of these arrows are longer than others. It’s that sweet spot! I want tight groups. If you want arrows that are perfectly matched by length, I understand. I can sell you that bamboo, or make those arrows for you. But you may be sacrificing your teacup group for a pie plate group. This is something that you might want to keep in mind when you set out to learn arrow making. Are they display arrows, or field arrows? Both are wonderful, and you can have whatever you want. After all, I do make custom arrows, right? Your goals are uniquely your own.,