What is F.O.C.? And how does it affect my arrows?

F.O.C. is a hot topic in arrow-building discussions today.

What is F.O.C.?

It’s the acronym for “front of center.” What it refers to is the percentage of an arrow’s total weight – including the point – that is concentrated forward of the center of the arrow.

F.O.C. is something that mainly bowhunters are concerned with, and there’s no question that having a solid F.O.C. number is key to getting good arrow penetration on a big game animal.

But some bowhunters think F.O.C. is the only factor they should be concerned with in preparing hunting arrows, and they don’t understand the consequences of simply beefing up the front end of their arrows.

Let’s start with a minimum. Easton Archery recommends arrows have a minimum F.O.C. of 10-15 percent. That’s going to allow an arrow to fly accurately, especially at longer distances. If you go less than 10 percent, the arrow’s trajectory will be flatter, but its flight will be more erratic.

That 10-15 percent is what Easton recommends for target arrows and for hunting arrows. The amount of weight needed up front to hit that range will be sufficient for hunting, according to Easton.

A lot of bowhunters today try to get their F.O.C. to 20 percent and even a little higher. They can do that by adding weight to their inserts. A standard aluminum insert might weigh about 16 grains, where there are brass inserts that can weigh 100 grains. Also, some insert manufacturers allow weights to be screwed into the backs of their inserts, which is another way to add weight to the inserts.

Gold Tip 100-grain brass insert

Bowhunters also can add weight by shooting heavier broadheads. A standard broadhead weighs 100 grains. But there are common options for 125 and 150 grains. And there are special broadheads aimed primarily at the heavy F.O.C. fans that weigh 200 grains.

Strickland’s Archery 200-grain broadhead

So if a bowhunter swaps out that 16-grain aluminum insert for a 100-grain brass insert, and trades a 100-grain broadhead for a 150-grain model, that hunter just increased the front-end weight of that arrow by 134 grains. That’s sure to boost the arrow’s F.O.C. considerably.

No question that arrow now will have improved penetration capabilities. But it also could cause problems for the bowhunter.

For starters, with all that weight added to the front of the arrow, the arrow’s spine is considerably weakened, and accuracy problems are likely. According to Easton’s hunting arrow shaft selection chart, an archer shooting a 29-inch arrow from a 62-pound bow should choose an arrow with a 340 spine while using a 100-grain broadhead. If the archer only increases point weight by 50 grains, that archer should be shooting a 300-spine arrow. The more weight you add to the front of an arrow, the stiffer that arrow needs to be to support that extra weight.

A second issue could be trajectory. When you add weight to an arrow, you slow it down, which adds more curve to its trajectory arc. For the Eastern tree stand hunter who expects most shots to be under 20 yards, that’s probably not an issue. But it could be for the Western hunter who is spotting and stalking and might have to shoot out to 60 yards. With that much weight added, a 2-yard miscalculation in shooting distance could easily result in a miss.

No question there are benefits to boosting an arrow’s F.O.C. to increase its capability of punching through an animal. Some animal hides are notoriously tough, and if the arrow hits a bone, it would be nice if the arrow could punch through that bone.

But as with many things in archery, balance is important. Kinetic energy is the amount of energy a body has in motion. It’s calculated by a formula that relies on the weight and speed of a moving object.

To calculate KE in foot pounds you would take the arrow weight and multiple it by the velocity squared, and divide that number by 450,800. For hunting game animals like antelope and deer, Easton recommends an arrow have KE values of 25-41 foot pounds. For elk, black bear and boar, Easton recommends 42-65 foot pounds.

To illustrate what an arrow build would be to meet those minimums, let’s look at the popular Easton Axis 5mm. A 29-inch, 340-spine arrow weighing 9.5 grains per inch, with a standard insert and fletchings would weigh about 315 grains. Add a 100-grain point and you get a 415-grain arrow. Shoot that arrow from a 70-pound bow drawn to 29 inches, and a speed of about 290 feet-per-second is likely.

The KE value for that arrow is 77 foot pounds. That’s well above Easton’s recommendation for any of those animals. So it’s safe to say that arrow is sufficient for bowhunting all of them.

The F.O.C. for that arrow is 12 percent, which is also within Easton’s recommended range. If I add a bunch of weight to the front of that arrow to try to get to 20 percent F.O.C., I am increasing the penetration capability of an arrow that already is capable to killing a deer, elk or black bear.

That’s not necessarily a bad thing. But remember to consider arrow spine and performance, along with your hunting expectations as you are building arrows with an eye toward boosting F.O.C.

A simple, inexpensive way to test arrow performance with different F.O.C. values is to get screw-in field points of varying weights. Saunders makes field points as heavy as 250 grains. Shoot several arrows with points of different weights at whatever you consider to be your maximum effective range. By doing this, you should be able to determine what gives you the tightest, most consistent groups.

Saunders 250-grain field point

Don’t just look for the tightest groups. You also want to consider forgiveness. That is, which arrows hit closest to your aiming point when you make a bad shot. If you have an arrow setup that produces 2-inch groups at 50 yards, but a slight bobble on your part throws the arrow off 8 inches, versus an arrow setup that produces 4-inch groups, with imperfect shots only missing by 3 inches, you should consider going with the latter setup.

How to build heavy hunting arrows

Heavy hunting arrows are wildly popular these days.

Whether you want just an overall heavy arrow or you want to add weight specifically to the front of the arrow to boost an arrow’s FOC, there are products that can help achieve your goals.

Let’s start with heavy arrows. Arrow weights vary wildly across manufacturers and individual shafts, but, generally, the typical weight for today’s hunting arrows is between 7 and 9 grains per inch, depending on the spine.

Once you get to 10 grains per inch and over, now you’re talking about some serious heavyweights. Easton’s 5mm FMJ arrow shaft in a 340 spine weighs 11.3 grains per inch, for example.

A 30-inch bare shaft would weigh 339 grains. By the time you add an insert, vanes and a broadhead, you could easily have an arrow weighing more than 500 grains.

Whatever you do, don’t simply increase the spine of the arrow you’re shooting in order to get a heavier arrow. That same Easton 5mm FMJ weighs 10.2 grains per inch in a 400 spine. If a 400-spine arrow is what your setup calls for, don’t choose the 340 simply to get more weight.

Stick to the spine recommendations for your draw weight and arrow length, since that will give you the best performance.

Now let’s take that heavy hunting arrow and add on a heavy broadhead. The 100-grain broadhead is considered standard, so maybe you increase to a 125-grain head, or maybe even 150 or 175. The Northern Broadheads Wide Cuts weighs in at a whopping 175 grains.

Northern Broadheads Wide Cuts 175-grain

But before you install that heavy broadhead into your heavy arrow, let’s swap out the standard aluminum insert that comes with your arrows for a brass one. Gold Tip’s standard, Accu-lite threaded insert for its .246 diameter arrows weighs 11.4 grains. But Gold Tip also makes a brass insert for its .246 arrows that weighs 100 grains. Simply swapping inserts boosts your arrow weight by 88.6 grains.

Gold Tip .246 Brass Insert

Black Eagle offers a stainless steel insert weighing 28 grains for its Spartan arrows to which you can add brass weights that weigh 30 or 75 grains. Those weights are the same diameter as the insert, and they have a threaded post which screws into the back of the insert. And they’re made so you can stack them, one behind the other.

Black Eagle Spartan 30-grain Brass Insert Weight

Other arrow and component manufacturers offer a variety of heavy inserts and insert weights to add weight to the front end of your arrows to boost the FOC. That stands for “front of center,” and it refers to the percentage of arrow weight that’s at the front end of the arrow.

Boosting an arrow’s FOC can help it stabilize in flight and to punch through hide, bone and tissue.

Understand, however, that when you increase the weight up front, you weaken the arrow’s spine. Most manufacturer spine charts make spine recommendations based on 100-grain points. If you use a 175-grain head with a 100-grain insert, you will want to go with a stiffer arrow.

So let’s take that 30-inch, 340-spine Easton FMJ that weighs 339 grains for the bare shaft. We will add Easton’s 75-grain stainless steel insert, and then screw in a 175-grain Northern Wide Cut. Before fletchings, we’ve got an arrow that weighs 589 grains and has an FOC of about 20 percent.

That’s a heavy arrow.

Lancaster Archery Supply has a full line of hunting arrows you can look through to compare weights and find the one that’s as heavy as you want it to be. We’ve also got a full line of arrow components that you can look through to find the inserts and points that will work for your arrow build.