Bowhunting: How to Find Your FOC
I was hanging out at the local archery pro-shop with the teens in my High School Archery club. The kids were having fun flinging arrows and poking holes in paper. I was chatting about different arrow setups with the shop owner, as will happen in an archery shop, and we were discussing the FOC of various arrow set-up we have used. After our conversation came to its inevitable conclusion, and young lady in the archery club called me over. “Mr. Grippa,” she said. “Umm, I heard you guys talking about your arrows, and I had a question.” “Sure” I replied, “What did you guys mean when you were talking about the FOC of your arrows?” That’s when I remembered that not everyone has been shooting a bow most of their lives and is as obsessed with this stuff as I am. So after I gave her a brief run down, it occurred to me that she probably isn’t the only person out there that may have the same question.
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What is the FOC of an Arrow?
First let’s talk about the acronym. FOC is short for Front Of Center. So what does that mean? It is referencing how much or what percentage of an arrow’s length is the fulcrum of an arrow in front of the center of the arrow. Simply put, how far is the balance point in front of the middle of the arrow? I assume most archers realize that the front of the arrow is the heavier end, but many may not realize that the FOC can make a difference in arrow flight and even penetration. More on that later.
Finding Your FOC
My guess is there are a lot of bowhunters that never think about or care to think about the FOC. They get their arrows cut, glue in the inserts, screw in the broadheads and never give it a second thought. If you’re like me and primarily hunt whitetails, that scenario works. A 100 grain head, and an insert in the front in will provide a good enough FOC to do the job. If that’s you and you aren’t worried about it, then you will can probably stop right here and move on to the nest article. If you think you may need to know how to find your FOC then please read on. So here is how to find your arrow’s FOC.
First step, measure the full length of the arrow. From the very back of the nock all the way to the tip of the head. Divide that length in half to find the center. Mark that spot with a pencil.
Next, balance the arrow on a relatively narrow plane. I usually use the back of the blade of one of my pocket knives. Once it balances mark the balance point of the arrow with a pencil.
3rd step is to then measure the distance from the balance point to the measured center of the arrow.
Finally divide that distance by the total length of the arrow, multiply that number by 100 and that will give you the percentage of arrow shaft the fulcrum is in front of the center of the arrow, or the FOC. For example let’s use an arrow that is 30” long. The center of that arrow is 15”. If the fulcrum or balance point is found at 12” from the front tip of the arrow then its 3” in front of the measured center. We then divide the 3” distance by the 30” length of the arrow to give us a FOC of 10%.
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What Does This Tell Us?
So now that we know how to find the FOC what does that tell us and what FOC do I need? Well that really depends on what you intend to do with that arrow. In my opinion an arrow that is being set up for a 3D target bow can have a different FOC then an arrow that is going to be used to hunt big game. You will find that opinions will vary but here is what I have found.
For an arrow I am going to bowhunt whitetails with it will have a larger FOC than my 3D arrow. I want my hunting arrows to have an FOC of at least 10% but I’d prefer them to be about 12%. A larger FOC means a little more weight up front and that arrow will deflect less. If I want it to penetrate and drive through bone, then I will strive to get that larger FOC. An arrow I’m building for a 3D set up is one that I want to have a flat trajectory. A smaller FOC will give me that, all things being equal. So what is the best for 3D? Great question. I have talked to guys that like theirs to be as small as 6% and others prefer 10%. Here is their line of reasoning. Small FOC equals flatter trajectory, that is true, but I have found that 5% to 6% and that arrow gets a little squirrely down range, especially in some wind. The people in the larger the FOC camp are concerned about hitting arrows in the target and deflecting out of the 12 or 11 ring. I think both are valid points, and that’s why I aim for the best of both worlds. I set my 3D arrows up to have an FOC of around 9%. I feel that it is happy medium between flight and deflection.
Hopefully this clears things up and you now know how to find the FOC of your arrows. I also hope that everyone now has better understanding of what the FOC of your arrow means for your particular set up. Happy hunting, shoot straight and I’ll see you in the deer woods.
Eric Grippa, GetZone.com Contributor