
Determining Correct Scope Base Angle 
At this stage I could have gone out and purchased a base with 30 MOA correction and be done. What I wanted to know was exactly how much I needed to shim under the rear base to get my elevation centered.
Now I needed to convert the MOA to a dimension that I could use at the scope base. While doing the math I realized this was another opportunity to explain MOA for those who might have trouble with it.
To better understand how this MOA thing works let’s go over some of the basic facts: the dimension of an angle can be defined as the length of an arc connecting two straight lines emanating from the same point.
A full circle has 360 degrees of angle. If we drew out all 360 degrees of a circle it would look like a pie with 360 pieces. Each one of these pieces would equal one degree. Or said another way… The angle formed by the two sides of one of these pieces would equal one degree.
One degree can be further divided into minutes of angle or MOA. There are 60 minutes of angle or MOA per degree. So if we take a one degree slice of this circle and divide it into 60 smaller slices, one of those slices would equal one minute of angle or one MOA.
So let’s look at the math for one MOA at 100 yards. 100 yards is the radius of our circle. And now we need the circumference of the circle so we can then divide it up into degrees and minutes of angle. The math formula for circumference is…radius x 2 x PI = circumference. PI equals 3.1416
So before we set up our equation let’s first convert our 100 yards into inches.
100 x 36 = 3600 inches
3600 x 2 x 3.1416 = 22619.52 inches
22619.52 inches is the circumference of a circle with a 100 yard radius. Now if we divide that number by 360 we get
22619.52 / 360 = 62.832 inches
So we can now say that a one degree slice of a circle with a 100 yard radius measures 62.832 inches at the curved out edge. If we now divide that slice into 60 more pieces, (remember there are 60 MOA per degree) we get
62.832 / 60 = 1.047 inches.
1.047 inches is the size of one MOA (minute of angle) at 100 yards. It is pure coincidence that one MOA almost equals one inch at 100 yards.
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