FOC stands for “front-of-center” in the archery world. The FOC represents the percentage of the overall weight of the arrow in the front half of the arrow. The greater the weight in the front half of the arrow, the greater the center-of-balance of the arrow.
One of the most significant factors influencing the form of the trajectory curve of the arrow is the F.O.C. balance position of the arrow. For target shooters competing in long-range shooting competitions operating under the Olympic Style rules, such as FITA Archery events, the ideal F.O.C is particularly important.
Although F.O.C is less important (short-range shots) in certain bowhunting circumstances, it can be crucial in others (long-range shots, when shooting low-poundage bows and fixing trajectory issues at the range).
Among archery experts, it is widely agreed that a high F.O.C. can fly with reasonable stability, but will shed its trajectory more easily and nose-dive. A low F.O.C. arrow can maintain its trajectory better, but it can fly erratically. For hunting setups and optimum accuracy, Easton recommends an arrow with 10-15 percent F.O.C., especially over long distances.
Calculating FOC For Arrows
Install all of the components that you will be using on the shaft (points/broadheads, vanes, inserts, nock, etc.) to evaluate the F.O.C of a hunting arrow. Your arrow is set up once:
- Split the total length of an arrow (distance to the bottom of nock groove to end of shaft by 2).
- Find the Point of Equilibrium. This is where it precisely balances the arrow. Label the point and weigh from the nock’s throat.
- Subtracting the middle of the measurement of the arrow (calculated in step 1) from the point of balance (calculated in step 2).
- Multiply by 100 the resulting number in Step 3.
- Divide the resulting number by the arrow’s total length from Step 4. The number is the F.O.C of your arrow.
If you find the F.O.C. of your hunting arrow to be unusually deviant from the recommended 10-15 percent range, consider adding/removing weight to/from the arrow’s front or rear.
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The balance of an arrow may be adjusted by adding weight to either the front or the rear of the shaft. For example, heavier vanes increase the weight of the rear portion of the arrow (decreases the F.O.C.). The rear of the arrow is lightened by substituting vanes with feathers. To change the weight of the front of the arrow, heavier points, inserts, and even added weights are used (increases the F.O.C).
Some bowhunters rarely aim past 30 yards, but a 10% to 15 % FOC is still recommended by Easton Archery. By adding or reducing the field-tip and broadhead weight, or inserting inserts within the shaft, you can adjust the FOC.
By adding or lowering the weight on the nock end, you may also control FOC. Although nocks, arrow wraps, vane sizes, and materials can seem to add minuscule weight, FOC is affected as much as the components in the front half of the arrow.
Do not get too carried away if you’re creating arrows or want to raise FOC in your existing arrows. You risk placing too much weight in the front half by adding 16% or more FOC to your arrows.
At longer distances or difficult to paper tune, that can make arrows nosedive. You still have time for FOC tests, with the hunting season a few weeks away. Consider crafting four settings for every dozen bows.
Fletch some with front lightweight vanes and additional inserts, as well as three- or four-fletch styles, and various field tips and weights for broadheads. Calculate the FOC of all four configurations, and shoot them side by side while noting changes in efficiency.
If you never take time to find the percentage of your FOC, you’ll never be as precise as you can be in the long range. Maybe your bow is tuned and your grip is perfect. If your FOC is too much or too little, you will struggle with distance accuracy, which will lead to issues of frustration and trust.
It’s not hard to find a FOC. It only takes a few measurements, finding a point of balance and some simple math. It takes a little math to find your FOC, but a NASA-pedigree isn’t required. First, make sure that the nock, broadhead, vanes and insert you’re going to be hunting with fits your arrow.
Your FOC will change if you find your FOC with a regular nock and then turn to a lighted nock. Lighted nocks are a tad heavier than normal nocks, adding weight to the shaft’s backend. Also, do not assess FOC with a field point of 75 or 100 grains and then turn to a hunting broadhead of 125 grains.