Minute of angle
From Gunsopedia
Minute of angle (MOA) is the measurement (in fractions of degrees) of a ballistic round's deviation from its initial heading due to gravity and/or the effect of air resistance on velocity. Informally known as a "Bullet's Trajectory" or "the rainbow effect". Long range weapons must account for this effect because a fired round falls at an exponential rate Weapons such as large caliber rifles use scopes with adjustments for distance and windage.
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