Firearms
This unit is commonly found in the firearms industry and literature, particularly that concerning high-powered rifles. It is popular because 1 MOA almost exactly subtends one inch at 100 yards, a traditional distance on target ranges. A shooter can easily readjust his rifle scope simply by measuring the distance in inches the bullet hole is from the desired impact point, and adjusting the scope that many MOA in the opposite direction. Most target scopes designed for long distances are adjustable in quarter (¼) or eighth (⅛) MOA "clicks". One eighth MOA is equal to approximately an eighth of an inch at 100 yards or one inch at 800 yards.
Calculating the physical equivalent distance equal to one minute of arc can be done using the equation: equivalent distance = (MOA ∙ 2 ∙ π ∙ distance)∕21600. In the example previously given and substituting 3600 inches for 100 yards, (1 MOA ∙ 2 ∙ π ∙ 3600 inches)∕21600 = 1.04719755 inches.
Sometimes, a firearm will be "measured" in MOA. This simply means that under ideal conditions, the gun is capable of repeatedly producing a group of shots that fit into a circle, the diameter of which can be subtended by that amount of arc. (E.g.: a "1 MOA rifle" should be capable, under ideal conditions and when locked into a vise, of shooting a 1-inch group at 100 yards.) However, ideal performance in a ballistics lab is often very different from real-world results.