Alright this time I’m going to attempt to further illustrate what MOA actually is. You have the thumb rule of 1 inch at 100 yards already, and that’s fine if that’s as in-depth as you want to go with it. But if you want to gain a better understanding of what this actually means, then continue reading.
How did we arrive at that 1 inch at 100 yards number? Let’s take a trip back to geometry class. If you never had a geometry class, that’s ok. You’ll just have to take my word for it I suppose? Let’s move on.
The diameter of a circle is the length of a straight line from one point on that circle to another point directly across from it, or 180 degrees away from it, since a circle is 360 degrees all the way around.
The length of the diameter of a circle divided in half is called the radius of that circle. Or, put another way, the length of a straight line from the exact center of that circle to the edge of the circle can be considered the radius also. So far so good?
Ok, so we know that a circle can be divided up into degrees, and is comprised of 360 of those things called degrees. Turns out, a degree can be divided further into even smaller units, called minutes.
That’s what a minute of angle is, it’s the smaller divisions of a degree, and 60 of these minutes of angle equals one degree. It’s that simple. A full circle is 360 degrees, a half circle is 180 degrees, and a degree is made up of 60 minutes. Cool? Cool.
So when we talk about MOA or minutes of angle in terms of shooting related shit, how do we determine what a MOA equals?
The distance you’d travel if you walked all the way around a circle is called circumference. Another way of looking at it would be if you took the circle and straightened out into a line, how long would the line be? Turns out circumference of ANY circle is equal to 2 times the number Pi times the radius of the circle. Pi is roughly 3.14. (This doesn’t have to be all that exact.)
So for the 100 yards example, let’s run the numbers and see what we come up with. If you’re shooting at a target 100 yards away, imagine where you’re standing or kneeling or sitting or whatever, is the center of a circle. And that 100 yards is the distance from the center to the circle itself, so the radius of this circle is 100 yards. We said that the circumference equals 2 times Pi times the radius. So when the radius is equal to 100 yards, our circumference all the way around this circle would be equal to 628 yards. Let’s convert that to inches. One yard is 3 feet. And one foot is 12 inches. So 628 times 3ft is 1884 ft. And 1884 times 12 inches is 22,608 inches. With me? Awesome.
We know that there are 360 degrees in every circle. And that each of those degrees is made up of 60 minutes. So if we multiply 360 times 60 minutes, we now know that a full circle is made up of 21,600 minutes.
So for our circle with a radius of 100 yards, we know the circumference is 22,608 inches. And since we also know that this circle is comprised of 21,600 minutes, we can figure out what the relationship between inches and minutes is for this circle. We simply divide the two numbers. 22,608 divided by 21,600 equals about 1.047 inches. Meaning there is 1.047 inches in every minute of angle for a circle with a radius of 100 yards. So is it really one inch at 100 yards? No, but it’s pretty damn close.
I hope that makes sense. It’s so simple but it confuses everyone at first. If it’s easier to just remember 1 inch and 100 yards and not where the number comes from that’s fine. I only put this out there in case anyone is curious about it.
The more important thing to remember is how to apply this. Meaning, at 300 yards, one MOA is now 3 inches. At 500 yards, 4 MOA is 20 inches. At 25 yards, two MOA is ½ inch. I care more that you understand that part than the derivation of the number itself. But as I said, I hope this was helpful.
I’m unsure of what to write about next time. We need to talk about other shooting positions besides prone so that’s probably what it’ll be. Til next time, take care comrades.