Arrow FOC | What is It and Why is it Important?
Bow hunters know and understand arrow speed. Today’s bow manufactures market speed as one of the factors that relate to a better bow. Speed, however, is only one aspect you should be focused on as a bow hunter. More importantly, arrow FOC is a factor that affects arrow flight and penetration, which is critical for any bow hunter.
What is Arrow FOC?
Arrow FOC – which stands for “front of center”, is the percentage of an arrow’s total weight that is located in the broadhead end of the arrow.
FOC is not as appealing as speed, but it is important when it comes to bow hunting. The more weight towards the broadhead end of the arrow, the more forward an arrow’s center of balance is and the higher its FOC will be.
FOC is a factor that comes down to balance. Arrow balance is important in bow hunting because it affects the shape of the arrow’s trajectory. Trajectory is critical for any bow shots out past 20 yards. The further your shot is, the more arrow trajectory matters. For long-range shots, or if you are using a low poundage bow, trajectory is a big factor.
High FOC arrows will shoot straight but lose trajectory (nose-dive) faster than arrows with less FOC. Shooting a low FOC arrow will gain back trajectory (flat shooting farther) but will be unstable and less accurate in flight. FOC also relates to penetration. Getting your arrow there with speed and trajectory is irrelevant if its penetration qualities are not enough to adequately take down your target. Outlining your potential bow hunting shooting scenarios helps to decide what the right FOC should be for your arrows. The most accurate arrows have a FOC range of 10 to 15% recommend by most arrow manufactures.
Calculating Arrow FOC is Easy
Unlike calculating arrow speed, which requires a chronograph, arrow FOC can be calculated with a few measurements and some simple math. You will need the following tools to calculate your FOC of an arrow; measuring tape, pencil, permanent marker, and calculator.
There are 5 simple steps in calculating arrow FOC.
- Choose an arrow that is completely put together, which means all components are attached such as inserts, broadheads, fletching, and lighted nocks.
- Use the pencil to balance the arrow on. Once balanced on the pencil, mark the balance point with the permanent marker so you can measure to that point.
- Measure from the bottom most point of the nock (the point where string touches nock) to the end of the shaft. This is measurement #1.
- Measure from the bottom of the nock to the balance point you marked in step number 2. This is measurement #2.
- Finally, calculating arrow FOC is done using the measurements and this formula: [100 X (measurement #2 – (measurement #1 / 2))] / measurement #1
The best FOC for hunting arrows ranges between 10-15%. Larger FOC arrows will carry with them more power and penetrate better than those with less FOC. Extreme FOC has rare hunting applications, those higher than 18% may pack a greater punch but become heavy and lose their aerodynamic properties quickly with increasing distance.
Why Arrow FOC Matters to Bow Hunters
Speed is a great thing but it only goes so far when you are a bow hunter. Speed should not be your only focus in the woods. But rather your objective as a bow hunter should be penetration and how well your arrows are set up to harvest game.
Two factors are at play when talking about penetration. The first factor is Kinetic Energy (KE), which is the energy your arrow has from being in motion. Momentum, the second factor, is the energy your arrow maintains as it meets the target. Both factors impact your arrow’s penetration ability. A lightweight arrow with low FOC has high KE but lower momentum at impact. Whereas a heavier arrow with higher FOC may have lower KE but packs more momentum, which penetrates more effectively through flesh and bone. High KE means you have plenty of energy in flight but without adequate momentum, an arrow has little ability to penetrate when meeting resistance. The higher the FOC, the more efficiently an arrow will transfer KE into momentum. Kinetic energy can be calculated by the equation below.
M= total mass of arrow (grains)
V= velocity of arrow (fps)
So how much kinetic energy should you aim for? The table below is a general recommendation of kinetic energy by type of game
There is a tradeoff, however. You have to compromise with FOC and its ability to penetrate. For example, you can setup for extreme FOC to something like 25% with a heavy broadhead. It would pack a heck of a punch, but it would have little KE (fly slower) and have terrible trajectory past 20 yards. The other extreme is to make a super light arrow with a low FOC. The arrow would have fast speed but almost no momentum energy for penetration. Bows today have such speed producing qualities that there is room to manipulate FOC to increase penetration without sacrificing distance and trajectory.
Techniques to Raise or Lower Your Arrow Weight and Arrow FOC
Obtaining preferred arrow weight and FOC and balancing it with speed can be done a number of ways. First, you can add weight to the point end of the arrow. For example, bump up your broadhead to 125 grains if you are shooting 100-grain broadhead. Also, different inserts like the Lock-n-Load® inserts from Nock Out® can help to change the dynamics of FOC. You may be reluctant to change the business end of your arrows so another way to up your arrow FOC is to lighten up the back end of the arrow. If this throws your FOC over the ideal percentage you can add more weight to the back of the arrow by dropping in heavier fletching, heavier nock, or lighted nock.
If you are comfortable with your total arrow weight, you can adjust FOC without adding weight by switching out fletching (style, length, and material) or switching out nocks, shaving weight off of the backend of the arrow and increasing your FOC.
Video – Lock-n-Load® inserts from Nock Out®
In contrast, you can decrease your arrow FOC by reducing your broadhead size or reducing weight to the front end of the arrow. Switching to a lighted nock (adding more weight to the back of the arrow) will add a few grains that can help to achieve your preferred arrow FOC.
Focusing on FOC rather than speed is tough for most bow hunters who have been trained on the premise that faster is better. Speed has its advantages in archery but when the time comes to make that kill shot, arrow FOC is just as important. Understanding FOC, kinetic energy, and building your arrows to maximize its properties makes for a highly stable, bone and muscle splitting arrow that will drop game in its tracks.