Most of what I have read was 8 to 16 foc I went with 12 by adding a 50 gr insert. Look on line and they give you the how to
Yes the FOC is important. The greater the FOC the more of the natural "arc" in your arrow when shot. Arrows should not fly perfectly parallel to the ground out to 50 yards (and they don't) therefore, by having a mid range FOC you will assist the arc in flight. A standard FOC should ideally be between 7-10% for hunting arrows with most expert arrow builders recommending 9%.
