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How to Calculate FOC

Front of Center (FOC) weight on an arrow can be the difference between hitting your target or missing it horribly. The added weight increases momentum, thus making it possible to be more accurate and attain deeper penetration. All three aspects—momentum, accuracy, and penetration— are absolutely necessary. 

“The goal of every bowhunter should be to achieve the most penetration as possible on an animal, with the intent of a full passthrough.” (Dr. Ed Ashby, 2019)

FOC is one of the most important factors.

Ideal FOC Percentages *

  • Normal FOC: Up to 12%
    • Target & 3D Shooting
  • High FOC: 12% – 18%
    • For small to large game
    • Rabbit, turkey, deer, elk, etc.
  • Extreme FOC: 19% – 30%
    • Large to extremely large game
    • Elk, black bear, wild boar, grizzly bear, etc.
  • Ultra-Extreme FOC: above 30%
    • Cape buffalo, elephant, etc.

*Because there are several factors, more or less FOC may be required for the animals listed.

According to Dr. Ed Ashby, bowhunting researcher who has invested 27 years in the study of arrow performance and broadhead lethality, these are the ideal FOC percentages. Read Dr. Ashby’s FOC research document.  It’s a fascinating research document on necessary factors for enhancing penetration in bowhunting.

How to measure FOC

  1. Shaft Length: Take the length of the arrow, from the throat of the nock to the back of the insert. This measurement should not include the length of your point.
  2. Balancing Point: This measurement could easily be taken by balancing the arrow on your finger; HOWEVER, it is more accurate to use a block of wood (triangular shaped) to assess the balancing point. The measurement is taken from the throat of nock to the balancing point.
 

FOC percentage is calculated using the following equation:

(ABP÷TAL – .5) x 100 = FOC Percentage

ABP = Arrow Balance Point

TAL = Total Arrow Length

Quick glance of the amount of FOC our BAD BOYS provide. This guide is based on a 32″ 3k Carbon Fiber Weave arrow with a 100 gr field tip.

Balancing point changes—and thus FOC percentages changes— when using different arrows and/or broadhead and field tip.

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Citations:

Ashby, Dr. Ed. “Dr. Ed Ashby’s Published Arrow & Broadhead Penetration Research.” Ashby Reports—Ashby Bowhunting Foundation, 2019, www.ashbybowhunting.org/ashby-reports.

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