Arrow F.O.C. Why Should I Care? – Arrow F.O.C. (Front of Center) is the percentage of an arrow’s weight found in front of its balance point. This is discovered by finding an arrow’s balance point, with the point you will be shooting installed, and marking it. Then measure the arrow’s overall length from the bottom of the nock string groove to cut-off point, determine the exact middle, and mark that. Measure the gap between these marks and divide by the arrow’s overall length (nock string groove bottom to cut-off point). Move decimal point right two spaces and that is your percentage.
The physics of setting an arrow into flight is a fascinating subject. When you release a bowstring, the energy imparted by your muscles and stored in a bow’s limbs and cams is then released into the bowstring. The bowstring then transfers that energy into the arrow as it parts ways and is launched into flight. As the arrow accelerates foreword, that energy continues traveling up the arrow shaft like an electrical current, and after a very short distance stops in the point and is carried there. Very cool stuff. Higher F.O.C. more efficiently carries that energy down range.
For field points, 9-11 percent is generally considered adequate to achieve reliable arrow flight while 12-14 percent is considered better while shooting broadheads. That difference in numbers should tell you something—higher F.O.C. creates additional arrow stability. Think of this in terms of a front-weighted barroom dart. The heavy front drags the lighter trailing portion of the dart straight into the target. The higher the F.O.C., the more stable and forgiving an arrow becomes, which means an arrow more resistant to impact deviances should you bobble a shot slightly or pluck the string on release.
Arrow F.O.C. Why Should I Care? – This added stability is especially pronounced when an arrow is subjected to a light deflection or side wind. For instance, say you hit a small twig or heavy grass stems while shooting at a deer. A higher F.O.C., or arrow with more frontal weight, will be less dramatically effected than an arrow with a lower F.O.C. or less weight up front. That arrow subjected to the light deflection, in other words, will still find vitals, instead of deviating wildly and missing or resulting in a wounded animal. In stiff crosswinds, a high F.O.C. arrow is also more likely to stay its course, the heavy front end dragging the trailing arrow into the bull’s-eye, contrasted against an arrow with a low F.O.C., which is more likely to begin whipping uncontrollably and miss the mark.
F.O.C. also directly effects penetration on game. Given the exact-same arrow and broadhead, and all other factors remaining equal, an arrow with a higher F.O.C. will always penetrate deeper on the same hit than one with a lower F.O.C. The heavier forward weight, more efficiently carrying all available energy, essentially drags the trailing arrow through the wound channel. This includes the ability to more effectively smash through heavy bone, granted the broadhead is of sturdy construction. To a point, higher F.O.C. also gives an arrow a higher ballistic coefficient (BC), to borrow from firearms/bullet terminology. Translated, this means high F.O.C. more efficiently carries energy at longer distances, while an arrow with a lower F.O.C. bleeds energy off faster at longer distances.
High F.O.C. is less critical to the average adult male shooting 65 pounds or more from a modern compound bow launching modern carbon arrows carrying kinetic energy in the high 70s to low 90s foot pounds, as we have energy to burn. But it does make a huge difference for those at the low end of the energy spectrum—youth, women, or traditional shooters—or those bowhunting especially large and sturdy big game such as moose, brown bears, African Cape or Australian water buffalo, hippo, or elephants.
Arrow F.O.C. Why Should I Care? – In the case of youth and women bowhunters, this can prove counter intuitive, as adding front-end weight often erodes launch velocity. Yet, more reliable results will follow if these bowhunters shun light 75- to 90-grain broadheads and instead choose a heavier broadhead. F.O.C. can also be boosted by adopting a brass or steel insert/outsert instead of standard aluminum, adding insert weights like those from Precision Design Products, or simply forgoing the standard 100-grain head in exchange for the old-standard 125- or 145-grain field point or broadhead. When dangerous game is on the agenda, broadheads weighing from 175 to 300 grains have become the go-to solution. Traditional bowhunters shooting less energy efficient longbows and recurves can also benefit from this program, increasing F.O.C. and overall mass to elevate momentum for more reliable penetration on game.
Aluminum inserts and 100-grain broadheads have long been the standard, but more bowhunters are beginning to see the advantages of heavier brass or stainless-steel inserts/outserts and broadheads weighing 125 grains or more.