October 19, 2022
By Chuck Adams
Just a few days before I wrote this, I had the pleasure of chatting with TV celebrity Kristy Titus at the Total Archery Challenge event in Park City, Utah. Kristy has an upcoming elk hunt and wanted to make sure her new 58-pound Bear Refine compound was set up for great penetration.
We looked at her setup, did a few calculations, and decided any elk inside 60 yards would be in deep trouble… Kristy is a great shot.
Serious archers like Kristy do not leave anything to chance when it comes to their equipment. They analyze every aspect, make adjustments as needed, and go hunting with confidence.
Bowhunters shooting heavy draw-weight setups tend not to worry about arrow penetration for bigger game. This isn’t necessarily true. However, lady bowhunters like Kristy Titus usually think about it more because their draw weights tend to be lower, their arrows lighter, and as a result their kinetic energy is oftentimes on the marginal side. But no matter what bow and arrow you shoot, there are factors that can enhance or absolutely ruin deep penetration with critters like caribou, elk, moose, mature black bears, wild boars, and a host of massive African species.
First, let me say there’s no such thing as too much arrow penetration. The more you can get, the better. Deep penetration improves the chances of an exit hole for greater blood loss to the ground. Even if your arrow doesn’t pass completely through, every inch of broadhead travel means more tissue damage and a quicker kill. The old notion that an arrow needs to stay inside a critter is bunk. Complete pass-throughs are best.
For an elk-sized animal (500 to 800 pounds), I believe pointblank arrow energy should be 50 foot-pounds or more. Kristy’s setup shoots a 330-grain arrow at 263 fps, producing 50.7 ft.-lbs. of energy. With her arrow slowing down about two fps per 10 yards of forward travel, at 60 yards the shaft would still have about 46 ft.-lbs. — enough to deeply drill an elk, if other factors are optimal. Let’s discuss those factors.
One thing I believe is overemphasized in penetration is shaft diameter. Arrow manufacturers often tout their skinny shafts as superior penetrators, but in my experience, this is seldom true in an animal — unless the arrow impacts heavy bone. Most arrow-penetration tests at the factory are made in artificial, clinging substances like ballistic gelatin. These have nothing in common with animal flesh and yield false results.
With most arrow hits on game, the projectile passes through ribs or soft tissue. The broadhead cuts a hole much larger than the shaft, and once that cut is made, the shaft slides along behind with very little friction. Shaft diameter — large or small —is not a factor. Blood, fat, and other slippery body materials lubricate the broadhead channel and lower shaft friction to almost nil.
Be it a fat 2413 aluminum shaft or a skinny 5mm carbon shaft with only two-thirds the outside diameter, both will penetrate about equal with the same broadhead. Penetration tests through leather and animal carcasses have proven this to me beyond the shadow of a doubt.
Small-diameter arrows certainly penetrate better through bone, like the edge of a shoulder blade, because bone clamps down on a shaft. Small-diameter shafts also track better in a crosswind. But in most cases, the difference in animal penetration is overblown.
One of the most important variables in arrow penetration is how well your arrows fly. It doesn’t take a rocket scientist to understand this. A clean-flying arrow puts all its power directly behind the broadhead in flight. On impact, that power pushes straight ahead to drive the broadhead deep. By comparison, a wobbling arrow sheds energy as it wags back and forth in flight. On impact, even more energy is flipped to one side.
Be sure your arrows cut bullet-holes through stretched paper from 10 or 12 feet away. If they tear paper up, down, left, or right, you need to tune your bow until those poor paper tears disappear. Then — and only then — will your hunting arrows achieve maximum penetration in game.
More than anything else, broadhead design will make or break penetration.
Think about it. If you attached a rubber blunt to your arrow, it would bounce off an elk. If you attached a streamlined, razor-sharp head with two narrow blades and a knifelike point, it would slice completely through a broadside elk. Same arrow, same kinetic energy, but very different results.
That said, it should come as no surprise that Native Americans bagged deer, elk, and other critters with arrows tipped by small, sharp, streamlined two-edge stone points. Their bows were crude and positively puny, with estimated arrow speeds below 150 fps and kinetic energy below 25 ft.-lbs. Yet slender arrowheads made the critical difference and fed primitive peoples for thousands of years.
Most bowhunters use broadheads with designs somewhere between a rubber blunt and a slender two-edge knife. For deer-sized game, heads with three or four blades and fairly fat nose sections will penetrate fine. So will mechanical, open-on-impact broadheads that expand rapidly and cut a huge hole. But for animals like elk, broadheads must be carefully selected.
Sure, mechanical heads like those offered by G5, Rage, and others will slice a giant wound channel through a whitetail deer. From a powerful 70 or 80-pound compound bow, these same heads might get the job done on a broadside elk, but all else being equal, a two or three-blade fixed head with a slender nose will penetrate much better on bigger game out of any and all bow setups.
Bowhunters often wonder what broadhead weight is best. Weight is not really a factor in animal penetration, but front-of-center (F.O.C.) arrow balance certainly affects flat trajectory and pinpoint accuracy. For the best of both, it is wise to shoot hunting arrows with a balance between 10 and 15 percent weight forward. Tests by Easton and others have proven this to be a great compromise between flat trajectory and consistent accuracy.
For a gal like Kristy, with very lightweight arrows, a 100-grain broadhead yields correct F.O.C. balance. With heavier arrows in the 450 to 550-grain range, 125-grain heads are necessary for proper F.O.C.
Deep arrow penetration in really big game is a must. Use a bow/arrow setup that produces at least 50 ft.-lbs. of pointblank arrow energy. Tune for perfect arrow flight, and then select a streamlined and low-friction broadhead. With these three factors, you might be pulling your arrow out of a tree after it blows through an elk!
Calculating Arrow Energy
To calculate the kinetic energy of your arrow, you need to know its velocity (speed) and how much it weighs.
Most archery stores have a chronograph you can shoot through to determine the speed. Any grain scale will give you an exact arrow weight — be sure your chosen arrowhead is attached.
From there, a simple formula reveals the precise energy: Velocity (fps) x Velocity (fps) x Weight (grs.) divided by 450,240 equals Energy (ft.-lbs.). For example, let’s say you shoot 500-grain arrows at 250 fps. Using this formula, 250 x 250 x 500 divided by 450,240 equals 62.47 ft.-lbs. With perfect arrow flight and a proper broadhead, you’ll probably shoot completely through a broadside elk or moose.
To increase arrow energy, crank up bow poundage and/or increase arrow weight. Arrow speed and flat trajectory will diminish with a heavier arrow, but kinetic ft.-lbs. will always increase.
You can follow Chuck on Instagram and Facebook at Chuck Adams Archery. Visit Chuck’s website at chuckadamsarchery.com.