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 isthe percentage of an arrow’s total weight – including the point - that isconcentrated 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 theyshould be concerned with in preparing hunting arrows, and they don’t understandthe consequences of simply beefing up the front end of their arrows.
Let’s start with a minimum. Easton Archery recommends arrowshave a minimum F.O.C. of 10-15 percent. That’s going to allow an arrow to flyaccurately, especially at longer distances. If you go less than 10 percent, thearrow’s trajectory will be flatter, but its flight will be more erratic.
That 10-15 percent is what Easton recommends for targetarrows and for hunting arrows. The amount of weight needed up front to hit thatrange 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.
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.
So if a bowhunter swaps out that 16-grain aluminum insertfor a 100-grain brass insert, and trades a 100-grain broadhead for a 150-grainmodel, 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 penetrationcapabilities. But it also could cause problems for the bowhunter.
For starters, with all that weight added to the front of thearrow, the arrow’s spine is considerably weakened, and accuracy problems arelikely. According to Easton’s hunting arrow shaft selection chart, an archershooting a 29-inch arrow from a 62-pound bow should choose an arrow with a 340spine while using a 100-grain broadhead. If the archer only increases pointweight by 50 grains, that archer should be shooting a 300-spine arrow. The moreweight you add to the front of an arrow, the stiffer that arrow needs to be tosupport that extra weight.
A second issue could be trajectory. When you add weight toan arrow, you slow it down, which adds more curve to its trajectory arc. Forthe 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 isspotting and stalking and might have to shoot out to 60 yards. With that muchweight added, a 2-yard miscalculation in shooting distance could easily resultin 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 arenotoriously tough, and if the arrow hits a bone, it would be nice if the arrowcould 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 bya 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 thoseminimums, let’s look at the popular Easton Axis 5mm. A 29-inch, 340-spine arrowweighing 9.5 grains per inch, with a standard insert and fletchings would weighabout 315 grains. Add a 100-grain point and you get a 415-grain arrow. Shootthat arrow from a 70-pound bow drawn to 29 inches, and a speed of about 290feet-per-second is likely.
The KE value for that arrow is 77 foot pounds. That’s wellabove Easton’s recommendation for any of those animals. So it’s safe to saythat arrow is sufficient for bowhunting all of them.
The F.O.C. for that arrow is 12 percent, which is alsowithin Easton’s recommended range. If I add a bunch of weight to the front ofthat arrow to try to get to 20 percent F.O.C., I am increasing the penetrationcapability of an arrow that already is capable to killing a deer, elk or blackbear.
That’s not necessarily a bad thing. But remember to considerarrow spine and performance, along with your hunting expectations as you arebuilding 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.
Don’t just look for the tightest groups. You also want toconsider forgiveness. That is, which arrows hit closest to your aiming pointwhen you make a bad shot. If you have an arrow setup that produces 2-inchgroups at 50 yards, but a slight bobble on your part throws the arrow off 8inches, versus an arrow setup that produces 4-inch groups, with imperfect shotsonly missing by 3 inches, you should consider going with the latter setup.