F.O.C. Here is a breif description and explanation for this:
Aluminum carbon arrows usually are tuned within a wide range of spine by using various point and insert weight combinations. Choose a insert and point weight combination suggested in manufacture specifications. Aluminum arrows can be point-weighted by 7% or 9%front of center, nib points, or by adding point weight systems to get weights between 7-9% or over 9% F.O.C. One thing to remember is the point and insert combinations are suggested weights and are a good starter point. If an arrow is too weak, use a lighter insert and point. If the arrow is too stiff, try a heavier insert and point. Continue to change insert adn point weight within the acceptable balance point range 7-16% F.O.C.
For recurve bows, another way of altering arrow spine is by adjusting the brace height. Increaseing brace height will make a arrow shoot weaker, and decreasing brace height will make it shoot stiffer.
Hope this helps someone out!
