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).

One so called "sight in" program makes the claim that changing a sight setting by 1 MOA won't change the bullet's impact point by the value predicted by the above paragraph, which is 3.141 inches at 300 yards. A simple example may help to show why this is in fact the correct answer. Normally there is some random variation between shots, which will be ignored in this example in order to keep things simple.

In this simplified example there is no need to know the bullet's velocity, BC, or even the sight height. All that needs to be known is that the gun is in a machine rest and the bullet is striking 11.78 inches below the line of sight at 300 yards. Also, assume that the same type bullet is fired at the same velocity on each subsequent shot. Changing the sight adjustment by 3.75 MOA (15 clicks at ¼ MOA per click) would drop (drop is correct) the sight line by 11.78 inches (3.75 x 3.141 = 11.78). Because the gun is in a machine rest, the next shot's trajectory would be identical, but now the bullet's impact point and the sight line exactly match at 300 yards.

So what happens if the sight line remains fixed on a target, and instead, the gun's barrel is elevated by 3.75 MOA? This small change in elevation has no discernable affect on the bullet's velocity or drop at 300 yards nor the time of flight. Because of this, the bullet's impact point would again coincide with the sight line at 300 yards; exactly as predicted. The only way this could not be true is if miniscule changes in the barrel's elevation caused significant changes in bullet drop at 300 yards, in this case. Elevating a gun's barrel is just like shooting up hill, and it takes a slope of almost 2 degrees (120 MOA) to cause just a 0.015 inch change in bullet drop at 300 yards, so a change of only 3.75 MOA of elevation could not have any noticeable affect on bullet drop.

The difference between most external ballistics programs is not the underlying physics or math, which has been researched and well understood for decades, its the usability and interface features. In that arena we feel Ballistic Explorer wins easily, and so do the many thousands of shooters who have purchased our program.