October 06, 2022
By Randy Ulmer
One of the most common reasons archers miss or wound deer is from the animal "jumping the string." This phenomenon may seem like a conscious effort on the deer’s part to duck the arrow, but it is merely an involuntary reaction to loud noise. The animal drops down to load its legs in order to sprint away from perceived danger.
In my last column, I discussed ways to make your bow quieter to minimize the volume of sound a deer hears. The thought process goes like this — the quieter the bow, the less likely the deer is to react quickly and violently.
In the next few columns, I will discuss whether making your bow faster will help in dealing with this issue. Obviously, the faster the arrow, the less time deer have to react. There is an ongoing debate as to whether making the bow faster is a good tradeoff, because the faster the bow, the noisier it tends to be.
Determining whether shooting a faster arrow is going to help significantly is a decision you must make based on many variables. It is important for you to be well educated before making this decision. This requires a discussion of scientific data as well as some empirical observations; I will also give you my opinions.
Sound and Distance Matter
The most important question is whether the deer is going to react immediately to the sound of the shot. This is dependent on the proximity of the sound to the deer and the volume of the sound. As I stated in the last column, we need to do everything we can to decrease the volume of the sound the deer hears. We can do this in two ways: by silencing our bows and/or by shooting from further away.
A sound source’s volume decreases with the square of the distance from the source. This means that the same sound energy from the source is distributed over a larger area, and the energy intensity declines with the square of the distance from the source. So, a bow will be four times as loud at 20 yards as it will be at 40 yards, and it will be 16 times as loud at 20 yards as it will be at 80 yards. Thus, the further away from a deer you are at the time of the shot, the less likely it is to react immediately to the sound.
Past a certain distance (for argument’s sake, let’s say 25-30 yards for the average arrow speed we shoot nowadays) it doesn’t matter how fast your bow shoots; an alert deer will have time to react before the arrow gets there. There are many variables involved in determining what this distance is, including the particular individual’s reaction time and attitude, the speed of the arrow and the size of the chest cavity. To reiterate, if the deer immediately reacts to the sound of the bow past about 25 or 30 yards, it doesn’t matter how fast your bow shoots an arrow, the animal will not be there when the arrow arrives.
When the bow is fired, the noise travels to the deer at about 1,100 fps. Once it gets to the animal, the inner ear must generate a nervous signal to send to the brain. The brain interprets this signal and produces a separate signal that travels down the spinal cord and out through the peripheral nerves and to the muscles. The muscles then take time to react to this signal to produce movement.
All of this takes time, although not all that much time. This relay system and how it works is well-known, proven science. What we are never sure of is how a particular animal will behave at any given moment in any given situation. So, if we want to do the math, so to speak, it all boils down to reaction times, which we can measure.
Reaction Time Impacts Aim Point
I’m a veterinarian and happen to know that all mid-sized mammals are built pretty much the same. Other than a few notable exceptions, all the bones and muscles in a human, dog or deer have the same basic functions and names. So, deer are much like us neurologically.
The reaction times of the fastest humans on earth — sprinters — have been well studied and thoroughly documented. To make sure there is no delay from the time the starter's pistol goes off until the sprinters hear it, speakers are placed very close to the runners. So, we can reasonably eliminate the variable of distance from the sound’s source to the ear of the runner.
Elite, world-class sprinters in the starting blocks take about .15 to .18 second to react to the starting gun. If a sprinter has a reaction faster than .1 second, he is considered to have anticipated the gun and it is regarded as a false start. Remember, too, that unlike a deer, sprinters have their muscles tensed and are already in the crouched position, ready for the sound of the gun. They do not have to drop down to begin their forward spring; they are primed and ready for the starting gun in all regards.
Field Editor Bill Winke, who is an expert on all matters related to whitetails and shooting, has studied many slow-motion videos of whitetail deer being shot at with a bow and arrow. He estimates a deer’s reaction time is approximately half that of an elite sprinter, so approximately .075 second.
The speed of sound is exactly four times as fast as an arrow traveling 275 fps, so the sound arrives well before the arrow. At 20 yards, it takes approximately .056 second for the sound of the bow to reach a deer, but it takes the arrow approximately .23 second to arrive. This leaves the deer approximately .17 second to react.
Winke estimates that at 20 yards, you need to aim about 6 inches low on a string-jumping deer with an arrow flying 230 fps, and with a 280-fps arrow you need to aim about 3 inches low. At 30 yards, you need to aim about 17 inches low with the 230-fps arrow, and about 10 inches low for the 280-fps arrow. These findings argue strongly for shooting a fast arrow; however, don’t run out and buy a faster bow or lighter arrows just yet, since there is much more to this story.
We’ll pick this topic up again next month.