Bullets and arrows do not fly straight but in a curve called a trajectory. Because projectiles have mass they are pulled towards the earth due to the force known as gravity. The further a projectile travels, the more pronounced its curve will become. This bend in the flight path is not symmetrical – it becomes more pronounced the further the projectile flies (Figure 1).
Bullets and arrows drop as they travel along the trajectory. The distance from you to your target (the range) thus has a critical effect on where your bullet or arrow will finally impact. The further you are away from the animal you are shooting at, the more you will have to compensate for bullet/arrow drop.
There is another force potentially influencing the projectile along its flight path and that is wind. The direction and strength of the wind will cause a lateral (sideways) deviation in the projectile and may also cause it to drop quicker because of headwind resistance. These effects on the bullet/arrow trajectory will depend on the strength and direction of the wind as well as the distance to your intended target.
It should now be apparent that estimating range accurately is critical to accurate shot placement and it is often not given the attention it deserves. Poor range estimation can result in a complete miss, or worse still, a wounded animal.
Estimating range to target is one aspect of the hunt over which the hunter has control. Effective range is the distance at which the hunter is confident that he can hit the specific spot he is aiming at. The moment doubt creeps into the equation, the shot is not on and the hunter should attempt to get closer or pass up the shot. Taking shots at ranges beyond the ability of the shooter is one of the most common causes of wounding. Associated with wounding by taking shots at too long ranges, is the common problem of errors of range estimation. Estimating range by eye is difficult and errors can result in incorrect shot placement.
Figure 1: A projectile follows a curve along its flight path as it is pulled earthwards by gravity.
There is more leeway in terms of range error estimation when using firearms, as they have a flatter trajectory. When using bows, however, even an error of a few metres can result in a complete miss or wounding. The answer is to shoot within the limitations of the weapon being used to hunt with, and to use the best method available to the hunter to ensure that a range estimate is accurate. Another reason why hunters attempt shots beyond what they or their equipment is capable of, is impatience. Limitations on time, physical endurance or frustration are often the “trigger” mechanism that will cause hunters to attempt shots at unacceptable ranges. Another factor that sometimes unfortunately creeps into the equation is ego. The hunter might feel embarrassed at returning to base camp to find that he is the only one in the group that has returned empty-handed. We must learn to be patient.
DIFFERENT METHODS CAN BE USED TO ESTIMATE RANGE:
Before the advent of modern tools for judging range accurately, hunters made use of what nature had provided them with – their eyes. The old hunters became pretty good at this but it required a lot of practice to become proficient in this skill and it was a case of trial and error. However, judging range by eye is the method most prone to error.
Using just the eyes, there are a few methods that can be used to judge distance:
– Use a known unit of measurement
Use a known unit such as the length of a cricket pitch, a tennis court or rugby field and see how many times this unit will fit into the distance between you and your intended target.
– Method of extremes
Look at your target and estimate what you think the maximum range to it is. Also estimate the minimum possible range. Take the difference and divide it in half to give you your final estimate. Example: You estimate the maximum range to be 280 m and the minimum to be 240 m. The difference between these two is 40 m. Half this is 20 m. Your final estimate is then either 280 m – 20 m or 240 m + 20 m, which will give you 260 m.
– Halfway method
The further an object is away from you, the harder it is to estimate range accurately. With the halfway method, the observer judges the distance to an object that appears to be half the distance to target and then doubles this estimate.
When estimating distance to target by eye there are certain conditions that will make the target appear closer or further than it actually is.
Conditions that make a target appear to be nearer are:
– a bright, clear day
– sun behind you (in front of the target)
– high elevations (target higher than the observer)
– large targets
– bright colours (white, red, and yellow)
– looking across ravines, hollows, rivers and depressions
– looking down long lanes, between rows of trees or mealies, etc
Conditions that make a target appear to be further:
– fog, rain, haze, smoke, dusk and dawn
– sun behind the target
– low elevations (target lower than the observer)
– small targets
– dark target colours (brown, black, and green)
– camouflaged targets (paint, netting)
Getting an accurate fix on range is important enough to invest some of your hard-earned money in a good rangefinder or riflescope.
Determining range with a rangefinder
There are basically two mechanisms that rangefinders use to estimate range – using the principle of split images and using laser technology. When activated, a laser rangefinder sends a laser beam to the target. It then bounces back from the target and back into the rangefinder. An internal clock measures the time taken for the beam to leave and re-enter the rangefinder and computes the distance automatically (Figures 2 and 3).
Split-image range estimation is less accurate, especially at longer ranges, but is better than judging by eye and is suitable for bowhunters that generally shoot at ranges less than 50 m. The instrument has two images that merge and become sharply defined when an adjustment knob is turned. The distance is then indicated in a small window. Split-image rangefinders, while a lot cheaper than laser rangefinders, have been rendered largely redundant by laser technology and may be difficult to find. I used one for many years and it was a great help to me.
Figure 2: The working principle of a laser rangefinder
Figure 3: Examples of commercially available rangefinders
Figure 4: Scope reticles that can be used to estimate range to target
Determining range with a riflescope
The theory behind determining range using a riflescope is the relationship between the angles of the reference marks on the reticle and the linear measurement of the target. Formally, it is called triangulation. Scopes used for estimating range are scopes with minute of angle (MOA) or mil-dot reticles (Figure 4).
The most commonly known of these “ranging” reticles is probably the mil-dot. Its name is derived from being graduated in mil, a mil being an angular unit of measurement. In a mil-dot reticle, the distance between the centre of the reticle and the centre of the first dot, as well as the distance between the centres of two consecutive dots, is equal to 1 mil.
If you know the size of your marks and the size of your target, you can easily calculate the distance. All you have to do is aim at the target, positioning the reticle to get the most accurate measurement possible. It is advisable to always measure the longest portion of target. If your target is a silhouette, for example, you should measure its height. This way, you will always maximise the accuracy of your triangulation.
Once you have taken the angular measure of the target, you can obtain the distance with a simple formula. If you work with metric units of measurement, you just have to divide the size of the target (in millimetres) by the number of mil it measures on the reticle, and you will obtain the range in metres. For example: You know that the abdominal area of a kudu measures about 500 mm x 500 mm. Aim at it with your scope and you’ll see that the target measures 1.5 mil (from the centre of the reticle, to halfway between the first and second dot, in a standard mil-dot reticle). Calculate 500/1.5 and your answer is 333 m, which is the distance from you to your target.
Almost all the ranging reticles are graduated in mil, but there are also MOA reticles on the market. If you have a MOA reticle, to calculate the range in yards, divide the size of the target (in inches) by the number of MOA measurements on the reticle, and then multiply the value by 100 (Figure 5).
In the example used above, the abdominal area of a kudu is roughly 20″ x 20″. If you look through your scope and see that this area takes up 6 MOA, the distance will be:
20 divided by 6 = 3.33. Multiply 3.33 by 100 and the distance to your target will be 333 yards.
A good hunter will make use of technology to estimate range accurately but will also practise judging range by eye in the event that his range measuring device fails, is lost or damaged, or he does not have time to use it in certain circumstances.