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General Questions


What Is MOA and Is It Really an Inch At 100 Yards?

MOA stands for Minute Of Angle. A full circle is divided into 360 degrees and each degree is divided into 60 minutes. Thus, there are 21,600 minutes in a full circle (360 x 60 = 21,600). A minute is a small angle, but it's exactly what's needed for gun sights. A rule of thumb is that changing a sight's elevation setting by 1 minute of angle changes the bullet's impact point by 1 inch at 100 yards. A more exact value and how it's arrived at is shown below:

A circle with a 100 yard radius (distance from the center to the edge) would have a circumference of approximately 628.32 yards or 22,619 inches (100 x 2 x pi = 628.32 {pi is about 3.1416}). Dividing the circumference in inches by the number of minutes in a full circle gives a value of about 1.047 inches (22619 / 21600 = 1.047). Thus, changing a sight's elevation setting by 1 minute of angle changes the bullet's impact point by 1.047 inches at 100 yards. And the bullet's impact point would change by 2.094 inches at 200 yards (1.047 x 2) and change by 3.141 inches at 300 yards (1.047 x 3).

MOA Diagram


What is SAAMI?

SAAMI stands for the Sporting Arms and Ammunition Manufacturers' Institute, Inc. SAAMI publishes a variety of standards for the production and testing of arms and ammunition. SAAMI is the standards setting body for ammunition and arms manufacturers in the U.S.A. With few exceptions, all commercial published ballistic coefficient (BC) values are based on the SAAMI G1 drag coefficient table or its derivatives.


What Are Standard Conditions?

Published downrange ballistics values for small arms usually use the following standard conditions:

Altitude: 0 feet (0 meters)
Temperature: 59 Fahrenheit (15 C)
Pressure: 29.53 inches Hg (750 mm Hg)

How Do I Get an MOA Value For Each Step Of an Iron Sight?

Knowing how much the sight adjustment is changed by each increment of your sights is important if you want to use Ballistic Explorer to its fullest. For guns with iron sights, you can make a few simple measurements and calculate how much each step on the ramp changes the sight adjustment. To get an accurate value, make careful measurements and record them in inches. First you need to measure how far the rear sight can move up and down. To do this, put the rear sight on the lowest step of its ramp, and measure the distance from the top of the barrel to the top of the sight's blade. Now put the rear sight on the highest step of its ramp, and again measure the distance from the top of the barrel to the top of the sight's blade. Subtract the first distance from the second to get the vertical movement of the rear sight. Divide the vertical movement by the number of steps in the ramp. This gives you the vertical movement per step.

The same procedure is used for sights with a screw adjustment. Turn the screw in until the rear sight is in its lowest position, and measure its height above the barrel. Next, turn the screw out 10 clicks (or increments) and measure the sight's height again. Now subtract the first distance from the second to get the vertical movement of the rear sight. Divide the vertical movement by 10 to get the vertical movement per click.

To get the sight base, measure the distance from the rear sight's blade to the highest point of the front sight. Finally, divide the number 3,438 by the sight base distance (in inches), and then multiply that number by the vertical movement per step. The result is how many MOA each step of the ramp changes the sight adjustment.

For example, on a particular gun, the rear sight's distance above the barrel in the lowest step of the ramp is 25/64 of an inch, while its distance above the barrel in the highest step is 33/64 of an inch. Subtracting 25/64 from 33/64 results in a value of 8/64. Any fraction can be converted into a decimal number by dividing its numerator (top number) by its denominator (bottom number); thus, the rear sight's vertical movement is 0.125 inch (8 divided by 64).

The ramp on this particular gun has 10 steps, so the vertical movement per step is 0.0125 inch (0.125 divided by 10). Next, the distance from the rear sight's blade to the highest point of the front sight is 19.2 inches. The number 3,438 divided by 19.2 is 179.1. The number 179.1 multiplied by 0.0125 (vertical movement per step) is 2.24. Thus, each step of the ramp changes the sight adjustment by 2.24 MOA.

 

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Last updated: 2014
Copyright 2014 by Dexadine, Inc.