In simplest terms, an arrow’s Front Of Center (or FOC) refers to the percent difference between the physical midpoint of the arrow and the actual balance point of the arrow as compared to the total length.
Understanding arrow FOC is important for many reasons, especially if the bowhunter chooses to shoot fixed-blade broadheads.
Most notably, arrow flight is directly affected by FOC, thus special attention should be given to it no matter what broadhead type is employed.
Also, the longer an arrow is in the air the more important Front Of Center proportions become.
Due to the amount of force being applied to the arrow as it is fired an arrow flexes as it leaves the bow. The fletching on an arrow works to correct this erratic flight and steer the arrow toward it’s intended target.
In order for this to occur efficiently, the fletching must rotate the arrow shaft around the physical midpoint of the arrow as quickly as possible.
Fletchings are more able to do their job when the physical midpoint of the arrow is farther behind the arrow’s balance point. This situation gives the fletching more “leverage” to work with.
Therefore if the arrow’s balance point and physical mid-point are too close together, or worse if the arrow’s balance point is behind the physical mid-point, the fletching will have a difficult time doing its job and the arrow will become unstable.
Recommendations For FOC
Generally speaking, FOC recommendations are 12 to 15% for broadhead-tipped arrows compared to 8-11% for field points. Bowhunters who shoot with fingers, and those shooting arrows less than 26-inches in length should lean more toward the 15% range.
This is necessary because shorter arrows tend to be inherently less stable, and finger shooters typically need more help correcting normal wobble upon releasing the arrow.
It should be noted that it is possible to shoot very accurate groups with field points when arrows have less than eight percent FOC, but consider that field points are more forgiving than broadheads.
When it comes to FOC it’s better to err on the large side. Studies have shown that arrows with a larger FOC carry more impact downrange and generally penetrate better. Don’t go overboard though (beyond 18 percent). Too much FOC will make arrows point-heavy and less aerodynamic downrange.
Calculating Arrow FOC
Figuring the Front Of Center on an arrow requires a little measuring and some basic math skills.
First, start with a tape measure and something to balance the arrow on (perhaps a pencil). Next, balance the arrow on the pencil and mark where the balance point is with a marker, pencil or piece of tape.
Then, measure the length of your arrow from the nock throat (where the string contacts the nock) up to the end of the shaft (where the insert goes in). Next, measure from the throat of the nock to the mark you made at the balance point.
Finally, input the figures into the FOC formula- [(ABP (arrow balance point) ÷ TAL (total arrow length) – .50] x100 = FOC. For example: If you had a 30″ arrow that balanced at 19″ the formula would read [(19÷30) – .50] x 100 = 13.3% FOC.
Correcting FOC Problems
What do you do if your arrow’s FOC is too low? First, try adding some weight to the point end of your arrow. This can be done by increase point weight from 100 to 125 grains or even using a heavier, often brass, insert. However, do so with caution.
Adding weight to the front of your arrow can change arrow spine, meaning a different arrow may be needed or, at the very least, re-tuning of your bow. Another option is to lighten up the rear of the arrow with feathers, shorter fletching or lighter-weight nocks.
If your front of center is too large you may try the opposite; remove weight from the front of the arrow or add weight to the rear.