F.O.C. Guidelines

Fine tuning arrow flight by using FOC. (Front of Center).  This method of fine tuning is something that not everyone knows about, but should.  By determining your arrows FOC percentage, you will be able to make changes/adjustments to help increase arrow flight stability and range.

In order for an arrow to fly correctly, with the point in the lead and the fletching following, the center of mass must be located somewhere between the tip and the middle of the arrow shaft.  If the center of mass is located close to the tip, the arrow will have good stability but will drop quicker because of the heavy nose.  However, if the center of mass is located close to the center of the shaft, the arrow will have good range, but arrow flight may be unstable.  As you can see the trade offs here are stable arrow flight vs. arrow range.  The object is to find a happy medium that will allow you to have the best of both worlds.

The balance of an arrow can be modified by adding weight to either the front or the rear of the shaft as needed. Heaver vanes, for example, increase the weight of the rear portion of the arrow. Changing points can add weight to the front of the arrow.

There is no perfect F.O.C. for each setup. Here are some starting points.

Common F.O.C.s for each style of archery.

FITA                11-16%

3-D Archery    6-12%

Field Archery 10-15%

Hunting          10-15%

Use the following formula to calculate the F.O.C. of an arrow.

L= Correct Arrow Length – Distance from bottom of nock groove to end of shaft.

A = Distance form the bottom of nock groove to finished arrow balance position (includes weight of point plus insert, nock system and fletching)

 AMO-Standard F.O.C. balance formula

F.O.C.%= 100x(A-(A-L/2)              
                 ------------------
                          L 

Example FOC Calculation

Balance Point Length   17.25”

Arrow Length                28”

Arrow Length / 2           14”

(17.25-(28/2))*100/28 = 11.6%

17.25-14 =3.25

3.25*100= 325

325/28=11.607%

If you would like to use Excel here is the formula: =SUM(17.25-(28/2))*100/28

To change a fraction to a decimal divide the lower number into upper number.

Example 5/16 divide 16 into 5 and you get .3125