Math doesn’t lie and you simply cannot overcome the reality of physics, not even with the fastest bow and well-marketed mechanical broadhead on the market.
So how can you maximize your archery skills this season? Do your math…seriously. Let’s go over some applied physics.
Kinetic energy as an indicator of a hunting projectiles ability to cleanly, ethically kill an animal, is worthless, as it measures the energy of a projectile at the point in time it leaves the weapon, not when it hits the animal. It also overemphasizes velocity relative to mass and does not account for important factors like drag, broadhead design and percentage of projectile weight front of center.
It was initially introduced as a way for bow manufacturers to market speed as the be-all, end-all measure of a hunting bow. What they failed to tell everyone is that shooting the soda straw they used to hit their marketed IBO speed at a living animal, especially one with heavy bones, is a recipe for disaster.
Momentum, if applied correctly to the example of bows and arrows, will measure your arrow’s ability to penetrate at point of IMPACT. It isn’t a perfect indicator of projectile efficiency because like KE, it doesn’t account for drag, broadhead design and percentage of weight that is front of center.
We’ll address those later. What is does give us though, is a great baseline to compare different arrow weight combos with all other variables being consistent.
Here is the math on a few hunting arrows shot from the same bow:
- Arrow 1: 350 grain arrow x 320 fps at point of impact = 112,000
- Arrow 2: 500 grain arrow x 270 fps at point of impact = 135,000
That means Arrow 2 has 20.5 percent greater momentum at the point of impact.
In order to get an accurate representation of an arrow’s ability to penetrate bone, you have to take a few other important factors. These things enable us to better quantify how much drag our arrow will have on a bone hit. Less drag equals better penetration. Consider these facts:
- The percent of arrow weight that is front of center
- Efficiency of broadhead design
- Bow and arrow tune, etc.
So maximum penetration is calculated as follows:
Adequately weighted arrow + high front of center + efficient broadhead+ properly tuned bow and arrow
Importance of Front of Center
Think of this in terms of the above illustration. Which projectile is harder to move of course in flight and penetrates the best at point of impact? The dart.
Moving more mass to the front of your hunting arrow creates a projectile with mass at the business end that will be more resistant to wind and far more forgiving to broadhead tune.
This has been the subject of countless articles and podcasts, and personally I don’t understand why. Which heads work the best and why seems pretty intuitive, and field trials bear out the obvious.
What we want is a strong, sharp broadhead that imparts a minimal amount of drag as it passes through tissue and bone.
Mechanical vs. Fixed Blade
Light, mechanical broadheads fail when they hit solid objects…like bone. The additional drag created by the flimsy blades opening at the point of impact, act like emergency brakes for your arrow.
They may cut a wide wound channel, but wide wound channels don’t result in quick, clean kills. A bowhunter’s objective is to deflate both lungs.
Single vs. Double Bevel vs. 3-blade
A single bevel blade creates rotation, much like adding a helical fletch. Matching the correct bevel with the correct helical direction will result in a very accurate, torque inducing arrow and broadhead combo. A single bevel head rotates through impact, acting as a lever when it meets a solid object like bone.
A single bevel at the end of an adequately weighted, high FOC arrow has been proven by studies like the one conducted by Ed Ashby, to be the best penetrating combo on bone hits. I shot cut-on-contact, single piece VPA 3-blades for a long time with great results. When testing on bone they don’t penetrate as well as a single bevel, but when paired with the right shaft, either out of a modern compound, or a recurve, I’ve shot them through ribs and shoulder blades and put plenty of meat in the freezer.
Cut on Contact vs. Chisel Tip
You want a broadhead that starts cutting the second it impacts tissue. Also, a narrow tip will impart less drag on a bone hit, increasing penetration.
Venting catches tissue, which creates drag. A solid broadhead is ideal.
A heavier broadhead creates a higher front of center arrow and increases total arrow mass, both of which result in a better hunting arrow.
Bow & Arrow Tune
Having your hunting bow and arrow perfectly tuned is imperative. When you screw, or glue, on a broadhead any tune issues will be amplified. The difficulty of tuning a fixed blade head to shoot out of a compound is the most often used crutch by proponents of mechanical heads.
The problem though is never with the fixed blade. The problem is somewhere in the bow and arrow tune. Most often the culprit seems to be that the hunter wants to shoot a light arrow and light head, not an ideal combo and very tough to tune. Other times it can be things like rest set up, nock fit or any other number of factors.
My Tuning Process
With both my compound and recurve I bare shaft tune and shoot out to 60-70 yards to make sure the bare shafts group with my fletched arrows and fly with the nock end in line with the field point from bow to target.
I don’t add broadheads to the equation until they do, and have never had a broadhead tuning issue following this process. You can also shoot them through paper but I always like to watch them in flight as well.
Heavy Arrow, Quiet Bow
Nearly every time I shoot my compound at the range I get a, “Man that’s a quiet bow, what are you shooting?” My answer is always “Your bow’s just as quiet, just needs a heavier arrow.” When you shoot light arrows, there is an excess of energy that reverberates through the bow because the arrow doesn’t have enough mass to absorb it.
When you add weight to your arrow it is able to absorb a greater amount of the energy generated by the bow, which results in less noise at the shot. Bowhunters know that less noise at the shot reduces the chance that the animal will move at release.
When you draw down on that buck or bull of a lifetime do you want to know, that if things don’t go as planned, your arrow will break through a front shoulder and deflate both lungs? If you do, swap the light arrow shafts and mechanical heads for a heavier arrow shaft and solidly built, cut on contact broadhead.
Good luck this fall!