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F.O.C. stands for Front of Center balance point. This measurement results from the relative weights of the components used in the arrow: shaft, insert, head, fletching, and nock. Let's talk about how to come up with the F.O.C. calculation:




Step 1. Overall length:
Measure the total length of the arrow from the nock groove to the tip of the arrow with the point you plan on using.



Step 2. Balance Point:
Install the tip you will be shooting. If you are testing stability for 3-D shooting put your field point into the arrow. Of course, for hunting install your broadhead. Find the arrow's balance point by sliding it back and forth along a fairly sharp edge. You'll find the spot where the arrow just balances. Next measure in inches from the bottom of the nock grove to balance point.  Then measure in inches the length of arrow from the nock grove to the edge of the arrow shaft (not the insert-also known as the cut length).  Mark it carefully. Now measure from the point of the arrow to the balance point and enter the distance above.



Step 3. Determine F.O.C.:
To find the F.O.C. (which is always expressed as a percentage) divide the overall length by two. This should produce the physical center of the shaft. Now subtract this number from the balance point and divide by the overall length. Multiply by 100 to express the fractional value as a percentage.

A projectile's flight is most stable when most of the projectile's mass is positioned Front of Center (F.O.C.). As such, an arrow should be heavier in the front than in the back. But how much? Where's the "perfect" balance point?

This is another hotly debated issue among archery enthusiasts. Some claim that F.O.C. makes little or no difference, others swear that F.O.C. has a profound effect on accuracy. Even the industry experts don't seem to agree, as the ballistic physics for F.O.C. include some rather elastic variables that make finding an "mathematically optimal" F.O.C. very difficult to declare and prove. To make matters worse, we even see a variation in how F.O.C. itself is calculated, depending upon which "expert" you ask. So while we have no interest in the fine points of the debate, we will agree that the tricky issue of F.O.C. is at least worth considering when purchasing a new set of arrows.

With all that said, it is generally believed that an arrow with a high F.O.C. will fly well, but with premature loss of trajectory (nose-diving). While an arrow with a low F.O.C. will hold it's trajectory better, but it will fly erratically. So again, another trade-off for you to consider.



So what should you be looking for?

It is generally agreed that the optimal F.O.C.% balance for an arrow is somewhere between 7% and 15%. In the example on the above, the 30" long arrow has balance point that is 3" forward of the arrow's actual center (15"). So it's F.O.C. is 3/30 or 10% - a reasonable F.O.C. balance.




How to determine the F.O.C. manually

How to determine the F.O.C. manually.  Take one of your arrows, fully equipped including tip, that you will be using. First you must find the balance point on the arrow's shaft. 

To do this..........

1) Try to balance the arrow on a sharp edge. 

2) Once you have successfully balanced the arrow, place some sort of mark at that spot on the arrow's shaft.
3) Next, measure (inches) from the bottom of the nock grove to the balance point. 
4)
Then measure (inches) the length of the arrow from the nock grove to the edge of the arrow shaft, not the insert (This is called the arrows cut length.) 
5)
Divide the arrow length by two, this will give you the physical center of the shaft. 
6)
Now subtract the physical center number from the balance point value and divide by the arrow length value. 
7)
Multiple this number by 100 to get a percentage (%).




 Balance Point Length 
 17.25"
 Arrow Length
 28"
 Arrow Length / 2
 14"
 Balance Point Length - (Arrow Length / 2)
 17.25 - 14 = 3.25
 3.25 Divided By Arrow Length
 3.25 / 28 = 11.6%



A F.O.C. value range of 7-10 percent is widely used as the best for a good balance between arrow range and arrow flight stability.  If your calculated F.O.C. doesn't fall with this range, don't stress out.  You can still have good arrow flight with an F.O.C. as high as 18 percent, but your range will not be as good.  Try not to go below 7 percent.


Weight:
  If you're concerned about your finished arrow weight or your F.O.C. balance it's worth mentioning that your choice and size of fletching material will have a significant impact on both of those attributes.  Take a look at the chart below to see how much your fletching choice will add to your finished arrow.  Since all of that weight is going to be concentrated in the rear of the arrow, heavy fletching material means a you'll also need more tip weight to maintain a good F.O.C. balance.

 

 Less Spine Required  More Spine Required
 Lighter Draw Weight
Shorter Draw Length
Lighter Tip Weight
Less Aggressive Cam
More Let-Off %
Less Efficient Bow
Heavier Draw Weight
Longer Draw Length
Heavier Tip Weight
More Aggressive Cam
Less Let-Off %
More Efficient Bow


click here >>Arrow Shaft Selector Charts







Good Luck and Remember "You Won’t Get’em if You Don’t Stick’em"©

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