The Heavy Arrow Advantage

By: James Nash

For the last several years, I have been trying to figure out how to make sure more of the elk hit with arrows get recovered. What follows is the result of lessons learned from guiding over 100 successful elk hunts. Shoot enough arrow.

The traditional bow crowd has embraced heavy arrows for a long time, but even when they transition to a compound bow, they let speed become the priority when they really shouldn’t. Bottom line is a heavy arrow fired from the same bow with the same broadhead will penetrate deeper than a lighter arrow even though the lighter arrow is going much faster.

The Science

This is a matter of physics. In the gun world, we rely on a metric called kinetic energy. Kinetic energy (KE) is basically the energy of motion. It is calculated as the product of mass x velocity x velocity, KE= MV². This is a scalar quantity measured in feet per pounds that describes the energy an object possesses due to its motion. The direction of that motion does not matter. When it comes to archery however, kinetic energy doesn’t tell the full story - we need to understand the momentum of the projectile as well. Momentum (P) is calculated as the product of mass x velocity, P=MV. Understanding momentum is basically an understanding of how much resistance is required to bring a given object in motion to a stop. In short, it is momentum that dictates the penetration depth of an arrow. Physicists enjoy coming up with strange units, so momentum is measured in Slugs.

Let’s use some of my personal archery setups as examples. I shoot a Prime bow with an 82lb draw weight and a draw length of 27.75”. My hunting arrow weighs 632 grains and its velocity is 265 feet per second. Therefore, its Kinetic Energy (KE) is 98.53 foot/lbs of energy (FPE) and its momentum is .744 Slugs. When I shoot 3D targets, I drop down to 525 grains and gain 25 feet per second to a velocity of 290 fps. My trajectory is flattened somewhat which allows me to take the unethically long shots common on modern 3D courses. For my target arrow, I achieve 98.02 FPE and .676 Slugs. What I have effectively done is flattened the arrow’s trajectory curve beyond 40 yards and kept roughly the same Kinetic Energy, but reduced the momentum by 10%. Think of it like this, if my hunting arrow penetrates 5” into a standard target, my target arrow only penetrates 4.5”. Even though my target arrow is going faster, it has less momentum and thus less penetration. Sometimes, you can drop arrow weight and increase KE but you will almost always decrease momentum. When it comes to penetration, momentum matters more than anything.

Don’t sweat the math, it’s the 21st century and the Internet is strong. Do a quick search for an arrow momentum calculator and input your total arrow weight and speed and it will spit this data out for you.

Time of Flight 

Now, I don’t believe string jump is a “thing” even though we have all heard about it and may have seen its effects in the field. Let’s be clear. If you make a sudden noise in the woods like the sound of a bow firing, an animal’s reaction is not the same as when you shoot a firearm at an animal. Here’s why: sound travels at about 1,100 feet per second (FPS) depending on density altitude. A whitetail deer’s reaction time is .16 seconds. I don’t care what bow you are shooting or how fast your arrow is, an animal is going to hear your shot before the arrow gets there. The noise they are reacting to is the sound of the arrow flying towards them. A moving object makes a different sound when it is going toward you than it does going away from you. Think of a truck passing on a road. It starts with a low pitch which increases in volume and tone until it passes you, then it gets quieter and lower in pitch. Arrow flight noise is unavoidable, but there are steps you can take to quiet your arrow down. Use four vanes instead of three, add three degrees of offset, and use solid broadheads that aren’t ventilated. These tips attempt to decrease air turbulence around the arrow, the underlying  cause of its sound.

Another advantage of increasing arrow weight is it decreases the sound your bow makes when fired. The sound your bow makes is excess energy it was not able to put into the flying arrow. Add more arrow weight and the bow makes less noise. So, what is the difference in time of flight on a 30 yard shot between a 290 FPS arrow and a 265 FPS arrow? .03 seconds, also known as, not enough to matter. The total flight time of the shot is .318 seconds for the lighter, faster arrow and 0.348 seconds for the heavier, slower arrow. With that, a deer has about 2/10ths of a second to move on a 30 yard shot no matter the arrow. Deer tend to drop down in order to load their legs and spring away from the object speeding toward them, therefore, aim low on the vitals. Elk tend to stand there and take it, aim where you want to hit them.

Trajectory 

Almost all bow hunters want the margin for error in guessing range to be as little as possible. Faster arrow speed reduces pin gap and thus, reduces the margin for error. I totally get that. To study this, I surveyed 600 hunters asking how far their last bull elk was shot at and averaged all the resulting distances. Conclusion: the average archery shot on a bull elk is generally 23 yards. We can use that as a likely engagement distance, but let’s say we need to plan on shooting 40 yards just for conversation. As a guide and lifelong hunter, I can tell you honestly that 40 yards on an animal is a really long shot. With that distance in mind, let’s go back to my personal bow shooting the two different arrows I previously described. The difference in impact between the 525 and the 632 grain arrows at 40 yards is 2”. TWO INCHES! That is not enough to miss the vitals of an elk or a deer with a center hold. I’ll take the 10% gain in penetration every time.

What about broadheads?

Over my years guiding, I’ve seen just about every broadhead on the market fired at animals. If you are hunting turkey or whitetail where penetration isn’t that hard to achieve, I say shoot whatever makes you happy. The exception is for the guys who likes to get really high in trees and might need to drive through shoulder blades, for them I say muscle up your broadhead.

The longer a broadhead is, the less work it has to do. Think of taking a kitchen knife and either stabbing or chopping with it. The stabbing motion will penetrate a steak with less force. What I’m describing here is called aspect ratio. If a broadhead is three inches long and one inch wide, it has a 3:1 aspect ratio and will penetrate easily. It is going to be super heavy at that ratio, but will glide through hide and ribs. Most broadheads on the market have a 1 ¼” – 1 1/2” cutting diameter and the overall length of the heads seem to be getting shorter and shorter. I know this tends to help stabilize arrow flight, but maybe look for longer broadheads and properly tune your bow to deliver them.

Single Bevel vs Double Bevel

Now for the big buzzword debate, single-bevel vs double-bevel blades. I pick single bevel blades for a couple reasons. It’s a stronger edge. That’s why single bevels are used on chisels, that edge creates torque (any force that tends to cause rotation). Torque breaks bones and creates a cavity that allows the rest of the arrow to pass through. It also helps stabilize the arrow in flight and reduces torsional forces in the arrow shaft during flight. Single bevel blades can get shaving sharp and are commonly used by sushi chefs.

In the past five years guiding elk hunters, the results have been made clear to me. 100% of my clients who shoot single bevel, single blade broadheads have had complete pass throughs. 100% of my clients who shot three or four blade broadheads have not gotten pass throughs. Pass throughs create two holes for blood to come out of and destroy all the soft tissue in between. That makes for dead elk.

A note on blood trails: elk that are shot through both lungs do not bleed well externally. Their chest is big enough to hold every drop of blood in their body. You’ll simply find them laying on the ground in 20-100 yards. I get nervous when is see an actual blood trail, as it tends to mean the shot placement wasn’t good.

Last year I had a client with a 70lb bow, shooting an Easton FMJ (great elk arrow) with a whopping 31” draw length. He shot a bull at 22 yards and the shot placement was money. Except he hit a rib. He was shooting an expandable broadhead and both blades were destroyed by the rib bone. The blades turned into anchors. He penetrated one lung with what basically amounted to a field point. We found he bull the next morning over 400 yards away. This could have been prevented with a single blade single bevel broadhead more suitable for elk.

Front of Center - FOC

Much has been discussed and misunderstood about FOC or the amount of weight forward of the center point of your arrow. In my opinion, 19% is a lot, 10% isn’t enough. Think of a hammer flying through the air like it was an arrow. If the hammer head hits first, the handle is going to follow the head and the target will absorb that energy in full. If the handle end hits first, the weight of the head will cause the hammer it to flip or drift to the side. Most of the momentum will shift in that direction. My advice is to shoot a heavy enough broadhead that your arrow weight balance is somewhere around 15% FOC. This will keep the arrow’s energy focused on the point of impact and penetration will increase dramatically.

Grains

There are 7,000 grains in one pound, 437.5 grains in one ounce. It seems like a big jump going from 100 grain broadhead to a 125 grain broadhead, but it really isn’t. I actually prefer 175-200 grain broadheads. There are catalogs full of options available for arrows, vanes, broadheads, bows, and all the Gucci stuff we can add to an archery set up. I see the broadhead as the critical point. It is the one piece of gear that can’t fail. Every other part of the system is about getting that broadhead to pass through the vital organs of an animal that will feed your family and stoke the coals of your memories for the rest of your life. Respect the broadhead. Use one with the proper edge, blade shape, aspect ratio, and weight to maximize momentum. The result will be more notched tags.