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Beginners fuss a lot over kinetic energy, as it’s no doubt an important figure. But for penetration purposes, momentum is arguably more important. Experienced bowhunters will tell you that it is ok to lose some speed and kinetic energy to gain more momentum with your arrows and I would say that they are correct. How can a slower arrow get you more result?
As you get more into hunting, it might be confusing at the beginning but once you get into it, everything becomes clear. You are hearing often those terms: IBO Speed (feet per second, FPS), Kinetic Energy (KE) (measured in foot-pounds per second), and Momentum (pounds per second).
All those terms are related to the arrows. The bows and crossbows are the objects needed to propel a projectile toward your target. Draw weight, lightness, quietness, accessories for accuracy and durability are some terms related to the bows and crossbows. That said, as long as you respect the minimum draw weight stipulated by your State or Province, the weapon itself is more about your personal preferences than really a game-changing factor while hunting.
Nowadays, bows and crossbows are so efficient that they don't become an issue for hunting success. However, arrows and its penetration factor are. It means that speed, kinetic energy, and momentum become the factors to take into consideration to increase your hunting success. Don't get me wrong here, bows and crossbows are still the most important piece of equipment you need for hunting but I am saying that to increase your hunting success, the arrow plays a bigger role than you might have thought.
The question remains, why experienced bowhunters would sacrifice some speed and kinetic energy over more momentum? Let's define some terms here before answering the question.
IBO stands for International Bowhunters Organization just to let you know. That said, the speed of a projectile propelled by a bow or a crossbow is determined by a chronograph. It is measured in feet per second to obtain the speed at the exit of the string when the arrow is released and not when it hits your target. Different poundage, draw length and arrow weight would affect that measurement. The IBO speed can be quickly affected by different settings, accessories, and physical characteristics.
This measurement is an indicator of a hunting projectiles ability to cleanly, ethically kill an animal. The minimum required to cleanly kill a target will depend on the size of the target and oscillate greatly. For instance, tough games like a moose need a minimum of 65 ft-lbs. of kinetic energy to assure you to have enough velocity to kill cleanly this type of target. It is an element to consider if you intend to hunt at longer distances. As you know, energy drops down with distance and you have to make sure that you have enough power even at 40 yards, for example, to ethically kill an animal.
On the other side of the spectrum, small games like rabbits would need a maximum of 25 ft-lbs of kinetic energy to be cleanly killed. The necessary kinetic energy oscillates greatly depending on the target.
Like mentioned previously with the IBO speed, the kinetic energy is also measured at the point in time it leaves the weapon, not when it hits the animal. It is really important to understand this element. High kinetic energy is a good thing because it means your arrow has plenty of energy. But without sufficient momentum, that energy quickly erodes upon meeting resistance.
The gravity and the air resistance cause the arrow drop and depreciate the velocity of an arrow, so to counterbalance this drop, you need to gain in momentum to increase the impact of your arrow. In other words, what you lose in speed should be compensated by more momentum (arrow penetration).
Momentum is the quantity of motion of a moving body, measured as a product of its mass and velocity. We find momentum in archery by using the formula of mass multiplied by velocity. In the case of arrows, you then divide by 225,400 to obtain the momentum value.
Momentum, if applied correctly to the example of bows and arrows, will measure your arrow’s ability to penetrate at the point of impact. It measures the energy ready to be transferred to your target. In other words, it determinates the penetration potential at downrange or what’s required to stop an arrow at a given distance.
For example, here is the math on a few hunting arrows shot from the same bow (pounds per second):
That means Arrow 2 has 20.5 percent greater momentum at the point of impact. This means that even at slower speed, the arrow has more energy (momentum) and will be 20.5 percent harder to stop at impact resulting in more penetration level and than more damage into the wound channel.
These results must be divided by 225 400 and would be seen as follows in momentum calculators:
Momentum is often forgotten or underestimated by many hunters and especially with beginners when we are talking about penetration. Of course, increasing your momentum instead of speed to expand your arrow penetration factor isn't the only factor while hunting to increase your success but will clearly generate a cleaner shot and than a more lethal shot. In other words, even a slower bow or crossbow with a proper arrow tuning will do the job and maybe a better job than the fastest bow or crossbow on the market.
For instance to understand with an illustration, which projectile is harder to move of course in flight and penetrates the best at the point of impact? Yes, the dart. The dart is the best example of heavier FOC to gain momentum and hit a target with strength and this, no matter the velocity of the dart.
All in all, as we saw above, two out of three factors tell you data when the arrow leaves the string known as the velocity (Speed and Kinetic Energy) of the bow or crossbow and only one tells you about the energy of impact which is the momentum, what actually really kills your target. Of course, it is all a combination of these three factors that will increase your hunting success but, momentum adds the extra "oomph" to assure you better results.
We can agree now that the arrow penetration is probably more important than the speed itself. Moreover, momentum is more important than speed and kinetic energy and this, simply because the momentum is the truly responsible element of a clean and lethal wound channel. Combined with the proper broadhead, the momentum is deadly.
The question is now, how it is possible to increase the arrow penetration without increasing the speed? Well, this article will help you with 6 ways to increase the arrow penetration for hunting purposes.
Let's say to obtain the maximum penetration, you should follow the following equation:
Adequately weighted arrow + high front of center + efficient broadhead + properly tuned bow and arrow = highly balanced arrow for hunting
The two first elements of the equation imply a heavier arrow weight for better performances. I chose to start with the Front of center (FOC) weight because of its importance.
By moving the FOC forward, it is moving more mass to the front of your hunting arrow creating a projectile with a mass at the business end that will be more resistant to wind and far more forgiving to broadhead tune.
It also allows the vanes to work more adequately over distance generating a more stable flight for the arrow.
Arrows manufacturers offer more and more commercially made hunting arrows with a wider weight range selection. If you consider shooting a heavier arrow shaft, if your carbon arrow shafts weigh, say, 7 or so grains per inch, consider swapping to something that weighs 9 or 10 grains per inch to increase the arrow overall weight to gain momentum.
Tip: without changing the spine of your arrows—is to add internal weight. You can buy commercially made weight tubing that fits inside your arrow and adds significant weight without altering the flexibility of the arrow. But there’s an easier, cheaper way: You can use plastic weed whacker line to do the same thing in your lighter arrow shaft.
The arrow spine is, basically, the stiffness of your arrow. The bigger the number, the more flexible the arrow shaft. A spine that’s too soft for your bow will keep right on flexing in flight, which of course can impede penetration. It is important to have the right spine because an arrow that isn’t absorbing enough of the bow’s energy at the shot might cause damage to your bow. For hunting purposes, a lower arrow spine like 340 grain versus 400 grain will be stiffer and store more momentum/energy to be transferred at the impact point.
There is a reason why Olympic archers shoot tiny-diameter arrow shafts combined with the proper arrow spine because they are more aerodynamic and less affected by wind drag. That same principle applies to hunting shafts. However, to shoot a small-diameter arrow shaft it requires specialized inserts and thus, specialized broadheads.
But, there are products on the market to fix that. These outserts from Clean-shot Archery allow bowhunters to use micro-diameter shafts in conjunction with standard 8-32 thread broadheads. The outserts weigh 50 grains, so you’re also adding weight up front and moving your FOC forward.
Move your 100-grain broadheads to a 125-grain points id not already done. Switching to a heavier broadhead not only increases the total weight of your arrow for more momentum, but it also increases your arrow's Front of Center (FOC), which is the total weight of the arrow forward of the balance point. That little extra FOC and this, without going crazy, can help your arrow's penetration potential.
The important aspect here is to find the sweet spot in-between balance arrows with heavier overall weight and unbalanced heavier arrows.
After switching to a heavier broadhead, the second step is to determine the right broadhead to decrease wind drag and increase penetration. What you want is a strong, sharp broadhead that imparts a minimal amount of drag as it passes through tissue and bone.
Mechanical vs. Fixed Blade
According to me, you should shoot a fixed blade broadheads. They support speed better and are more strong. Razor sharp blades to deflate both lungs to clean kill your target. Keep it as simple as possible so fewer things can go wrong while hunting. Mechanical broadheads are efficient but more susceptible to fail on bones.
Single vs. Double Bevel vs. 3-blade
A single bevel blade rotates through impact acting as a lever when it meets a solid object like bone. With to right tuning, these broadheads will result in a very accurate arrow.
Cut on Contact vs. Chisel Tip
Last question. To increase penetration, you should choose a broadhead that starts cutting the second it impacts tissue. Also, a narrow tip will impart less drag so cut-on-contact should be prioritized to those with a chisel tip.
They have the very least resistance of any broadhead style and so, as a rule, tend to penetrate best.
Momentum is the keystone of arrow penetration and hunting. As you saw in this article many little improvements can be made to increase an arrow penetration factor without changing or purchasing the brand new bow or crossbow that shoots at 400 FPS.
To ensure hunting success, increasing your arrow penetration will deliver better results as if you increase your speed instead. Keep that in mind when you intend to purchase a new bow or crossbow.
Thank you for reading us. Do not hesitate to leave any comments or questions below about this article arrow penetration: 6 ways to increase it for hunting.
Have a nice Hunt!