Topic of the Month: June
2001
What is Minute Of Angle (MOA)?
MOA or minute of angle is a term often used by shooters
relating to sight adjustment or to explain bullet height in relation to the horizontal at
various ranges. It is usually understood that one minute of angle is about one inch at 100
yards.
True minute of angle is measured by first determining the
minutes of angle in a circle. We know that a circle contains 360 degrees and that there
are 60 minutes in each degree. The minutes of angle in a circle is 360 * 60 or 21,600. The
circumference of a circle is 2 * p * R where R is the radius of the circle in inches. Hence, for any
range R, a minute of angle equals 2 * 3.1416 * R divided by 21,600 or .000291 * R.
Therefore, if the range R is 100 yards, a minute of angle
would be .000291 * 100 * 36 or 1.0476 inches. Because the distance covered at 100 yards is
so close to being exactly 1 inch, the fraction is usually disregarded for range work, and
we commonly say that a minute of change on the rear sight will move the point of impact
1-inch at 100 yards. If we were shooting at 1,000 yards, a minute of angle would cover
.000291 * 1000 * 36 or 10.476 inches. The difference between the true minutes of angle and
the rounded minutes of angle becomes greater as the range increases.
Watch our web site for the next topic of interest "How
Important is Rifling Twist." Until then, shoot safely and know where your bullets are
going.
Sincerely,
The Ballistician
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