This sample chapter from the Long Range Shooting Handbook is Chapter 9, Units of Measurement. In this chapter I introduce yards, maters, MOA, Mils, velocity, ballistic coefficient, and more! These topics are explored greater (how to actually use them) in other sections of the book. Below, you’ll find just a preview. If you want to read the whole chapter, subscribe to my newsletter at the bottom of the page. After doing so, you’ll be able to view the content of the entire chapter on this page and you’ll also get a pdf version emailed to you. Enjoy!
9 Units of Measurement
There are many measurements that we must take into consideration when shooting long range: distance to the target, size of the target, elevation compensation, windage compensation, barometric pressure, temperature, and others. You need to get familiar with all of them, as we need to speak the same language.
9.1 Linear Measurements. Linear measurements are generally used to describe the distance to a target. However, they are also sometimes used to describe a target’s size for range estimation purposes.
9.1.1 Yards (yds). A yard is an English/Standard unit of measurement and it equals exactly 3 feet (36 inches).
9.1.2 Meters (m). A meter is a metric unit of measurement and it is the basic linear unit in the metric system. From this unit of measurement, prefixes are added to describe different lengths. For example, since the metric prefix for 1000 is “Kilo,” 1000 meters is 1 Kilometer. Likewise, “Centi” is the metric prefix for 1/100th and therefore 100 Centimeters make up 1 meter.
9.1.3 Converting Between Yards and Meters. There is about a 10% difference in size between yards and meters. To be accurate, 1 meter equals 1.09 yards and 1 yard equals 0.91 meters. This means that there is actually closer to a 9% ifference, but for simplicity’s sake, I prefer to just use 10% since I can easily calculate 10% of a number by moving the decimal place one position to the left.
For example, to find 10% of 450.0, move the decimal point one spot to the left for an answer of 45.0.
The ability to calculate percentage in your head is better than relying on a calculator in the field. If I want to convert meters to yards, I add 10% and if I want to convert yards to meters, I subtract 10%. For example, to convert 500 yards to meters, I move the decimal place one position to the left and end up with 50.0 as my 10% figure. I then subtract that 10% figure from the original 500 and end up with 450. This means that 500 yards is approximately 450 meters (note: actual conversion is 455 meters). (See Figure 9.1-1).
Notice how the number for the meters is smaller than the number for yards. This will always be the case and it is a good way to confirm your math, when you’re cold, tired and hungry.
SECTION QUIZ (answers at end of chapter)
- Which unit of measurement is longer, a yard or a meter?
- When converting from yards to meters, will the number for meters be larger or smaller than the number for yards?
- 900 yards equals approximately how many meters?
- 420 meters equals approximately how many yards?
9.1.4 Linear Conversion Charts The following charts (Figures 9.1-2 and 9.1-3) are used for converting linear measurements.
9.2 Angular Measurements Angular measurements are used to describe linear size relative to distance. The most common uses are incremental adjustments to the bullet impact, estimating the distance of a known-size target, “holding” for windage or elevation, and measuring accuracy by shot-group size.
The most important thing to understand about these measurements is that they are angular! For example, when we adjust our scopes, we move the reticle inside the scope which then forces us to move the barrel of the rifle up, down, left, or right in order to get the reticle back on to the target. This difference between where the rifle’s barrel was pointed prior to an adjustment in windage or elevation and where the barrel is pointed after the adjustment is a change in angle.
This same angular adjustment translates into smaller changes in the bullet’s impact at closer distances and larger changes at further distances. To help you understand how an angular measurement translates into a different sizes at different distances, imagine holding two laser pointers next to each other and pointing them down range. If you spread the two laser pointers apart at a certain angle, the lasers would gradually get further and further apart from each other as they went down range. For a certain angle, however, the rate at which the dots spread apart is consistent. The dots will be twice as far apart at 200 yds – and ten times as far apart at 1000 yds – as they were at 100 yds. See Figure 9.2-1. 9.2.1 Minute of Angle (MOA) In the term Minute of Angle, the word “minute” means 1/60th (for example, there are 60 minutes in 1 hour so 1 minute of time is 1/60th of 1 hour) and the word “angle” refers to one of the 360 degrees in a circle. So, 1 Minute of Angle is 1/60th of a degree. See Figure 9.2-2. If we spread two laser pointers apart 1 MOA (1/60th of a degree), the dots would be about 1 inch apart at 100 yards, about 2 inches apart at 200 yards, about 3 inches apart at the 300 yards and so on. Simply stated, this means that 1 Minute of Angle is . . . (to keep reading, subscribe below!)