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).

Contrary Claims

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. The claim centers on the concept of a "vertical velocity" being caused by the barrel being pointed slightly up when the line of sight is horizontal, but this is easily disproved at the shooting range. Simply place two targets 100 yards down range with one target several feet higher than the other. If the theory were correct, shots on the upper target would always group significantly higher relative to the target's center than on the lower target. In practice you won't be able to distinguish any difference until the vertical distance between the two targets if over 50 feet, and even then it has nothing to do with vertical velocity.

The vertical velocity is just an illusion that comes from measuring the trajectory of the bullet relative to the location of the muzzle, which is simply wrong. When the bullet's trajectory is properly measured relative to the line of departure it's evident that the bullet begins to drop as soon as it leaves the barrel. There is no vertical velocity apart from that caused by gravity. Ballistic Explorer employs a sophisticated three dimensional ballistics engine that properly handles all such situations and it's proven accurate in real world conditions, and that's where we all shoot.