Bowhunting Physics for Hunting Hogs

by Kevin Reese

Before you know it, turkey season will fade into little more than good memories… or at least unadulterated frustration. And once it does, scores of hunters believe there is little else to do but endure the long, seemingly endless wait until the fall archery opener. During such periods clocks slow and days drag on; the wait can be excruciating and, if not for a little arrow slingin’ with buddies, downright maddening. Fortunately a growing population of hunters are learning that the close of one season simply means it’s time to shift focus to another challenging pursuit.  One that is sure to test your skills and fill your freezer is hog hunting.

The Hog “Prob-ulation”

While many argue whether hogs are considered varmints, predators, exotics or big game; all would agree hogs can get extremely large, are incredibly intelligent, exceedingly vicious and maybe even a tad aggressive. Of course, many hunters also know how great hog meat tastes and just how invasive and damaging these marauders can be. The inconvenient truth is that we have a significant hog “prob-ulation”. They continue to invade new regions of the country and are now being reported in at least 39 states and four Canadian provinces.

In my home state of Texas, home to an estimated 50-percent of the nation’s feral hog population, as well as many other states, hogs can be hunted day and night with rifles, shotguns, handguns, bows, knives, dogs, thermal imaging, night vision and other means. (Be sure to check your local hunting regulations.) For me, there is nothing sweeter than the thrill of victory while wielding a stick-and-string!

Physics for Bowhunting Hogs

Taking a wild hog with a bow is not just exciting, it’s quite a challenge. Unlike deer, hogs have a tough hide, layered in fat and covered by extremely coarse, hollow hair. Worse, as a result of fighting through the years, mature boars develop a thick, protective cartilage plate, also known as a shield, which protects their vitals. When bowhunting for hogs, kinetic energy (KE) and momentum (penetration) are critical. Bowhunters must understand those two key elements before hitting the hog woods.

KE, put simply, is the amount of energy your arrow has as it impacts your target. It’s based on a simple formula that combines arrow weight and velocity to quantify energy in foot-pounds (ft-lbs). However, performance does not stop with KE. Momentum, expressed as slug ft/s, should also be a key factor in optimizing a hunting setup for hogs. This is especially true because while KE packs energy, momentum packs punch, penetrating those vitals. The difference is that KE focuses on velocity while momentum focuses on mass. Skilled archery technicians, given simple math formulas, can help you come up with an arrow setup capable of delivering the optimized results of both KE and momentum.

If the idea of figuring KE and momentum into your archery setup have your head reeling, consider this. Generally speaking, 60 to 70 pound draw weights on a modern hunting bow, with appropriately spined arrows and run-of-the-mill broadhead weight of 100 grains are more than enough to get good penetration on mature boars.  This is especially true on quartering away shots where the arrow is placed far enough back in the body to sneak in behind the shield.

For those willing to dig into the physical science behind their setups and optimize performance, the easiest ways to find the perfect combination are through running calculations using different arrow selections and draw weights.  Using a 378gr arrow traveling 303 fps velocity we get the following numbers:

Kinetic Energy (ft-lbs)
KE = Velocity2 x weight / 450,240
91,809 x 378 = 34,703,802
34,703,802 / 450,240 = 77
KE = 77 ft-lbs
*NOTE: Emphasizes speed (450,240 is constant)

Momentum (slug ft/s)
M = weight x velocity / 225,400
378 x 303 = 114,534
114,534 / 225,400 = .51
Momentum = .51 slug ft/s
*NOTE: Emphasizes weight (225,400 is constant)

Penetration depends on three factors – momentum, the broadhead, and what you are cutting through. Obviously+ you experience less penetration when hitting bone than you ever would simply carving through meat, muscle and other tissues. Neither broadhead type nor blade quality affect KE but they most certainly can and do affect momentum and resulting penetration. Common sense tells us that two arrows tipped with broadheads, one sharp and one dull, or to go a step further, one with a cutting diameter of 2-in. and the other at 1 1/8-in., deliver exceedingly different penetration results. This dynamic relates precisely to Newton’s Third Law of Motion which is that for action, there is an equal and opposite reaction.

Considering Newton’s Third Law of Motion, there is a distinct difference between hog and deer hides. While I may choose to use a sharp mechanical broadhead with great results on the thin hide of a deer, I typically choose not to use mechanical broadheads on hogs.  Their tough hide and tough hair absorb much of the energy from your arrow on impact, and a large mecahnical broadhead may not penetrate as well as you would like.  For wild hogs I choose broadheads with at least .040 blade thickness for tough work. No matter what you choose, make sure your broadheads are razor sharp! Also ensure your arrows are of correct spine, true to the allowable tolerances of the manufacturer, and that your bow is tuned properly to optimize arrow flight. The flight of your arrow certainly does impact penetration.

If you live in or near one of those 39 states or four Canadian provinces, your season does not end with the amber glow of a sun sinking on the horizon. To the contrary, add a light system to your bow and try night hunting for hogs. It’s a little payback for those super-slick hogs that try to play the nocturnal game. Daylight or dark, hog hunting provides some of the funnest – and tastiest – hunting opps of the year. Pound for pound, you’ll rarely find a more enjoyable live target to chase in the off-season. Get out there and give it a try this summer.