FOC, or Front of Center Balance, describes the percentage of the arrow’s total weight that is located in the front half of the arrow. The more weight that is located in the front half of the arrow, the more forward is the arrow’s center-of-balance, and the more stable the arrow flight- up to a limit.
Arrows with a negative FOC value are inherently unstable in flight. However, excessive positive FOC balance can lead to an unpredictable “nosedive” at longer distances, as the arrow loses speed.
Higher FOC balance, within limits, can also improve performance in side-wind conditions. Optimal FOC is most important for target shooters participating in long-range shooting competitions, especially past 50 meters.
Variables affecting FOC balance are the arrow shaft mass, the point/insert mass, and the mass of fletching and nock. For example, a lighter arrow shaft with a 100 grain point/insert and light weight fletching will have considerably more positive FOC balance than a heavier shaft with the same point/insert weight of 100 grains and heavier fletching.
In bowhunting applications, the actual FOC balance is already likely to be well within a usable range, due to the mass weight ranges of most broadheads and inserts combinations, along with the mass of most arrow shaft options suitable for hunting. Excess FOC will also cause a given arrow to have a lower dynamic spine, which can cause problems for tuning.
Having a particular FOC is less relevant in most typical bowhunting situations (short-range shots), as long as the FOC has a positive value, but a somewhat higher FOC value becomes important for longer-range shots, especially when shooting lower-poundage bows.
Target FOC range
Generally, for target archery, an F.O.C. range of 7-15% indoors, and 10-15% outdoors, will fly with good stability, optimal momentum, and accurate trajectory from 0-90 meters. Past this range can cause vertical dispersion at longer distances, especially with lower overall mass arrows. Excessive FOC (especially past 20%) can also make finger release consistency much more critical, as the inertia of a too-heavy point can make the arrow over-react to slight differences in finger release. Arrows with lower FOC values (under 7-10%) will not track as well in outdoor windy conditions.
Bowhunting FOC Range
Easton recommends a 10-15% F.O.C. for hunting setups requiring greater momentum, and optimal accuracy – especially for longer distance shots.
