how does MOA work?

huntin4em

huntin4em

New member
I am not really knoweldgeable about ballistics, and was wondering if anyone could give an idiot proof explanation of the basics of how it works? Thanks for reading!
 
The angle of an arc is expressed in number of degrees. There are 360 degrees of arc to a full circle. Each degree consists of 60 minutes of arc. The distance covered by the measure of arc is relative to the circumference (total distance around the circle) it is contained within. Knowing the radius (distance to center of circle) circumference is easily calculated by using the constant pi . The ratio (represented by pi ) of circumference is constant to diameter (radius x 2) regardless of circle size. The precise value of pi is so far unknown to man but is normally resolved to 3.1416 or 3.141 for our purposes.


Suppose a circle with a 6 inch radius. Circumference can be calculated as:

circumference = (radius x 2) x pi
circumference = (6 x 2) x 3.1416
circumference = 12 x 3.1416
circumference = 37.6992 inches

The distance covered by 1 degree of angle (37.6992 / 360 or, circumference divided by 360 degrees) is 0.1047 inch at 6 inches from center of circle.
And, 1 minute of angle represents (0.1047 / 60 or, 1 degree divided by 60 minutes) 0.001745 inch at 6 inches from center of circle.

Knowing what MOA represents allows us to calculate its value to any distance.
Six inches (the radius of the above example) is 1/600th of 100 yards: (100 yards x 36 inches) / 6 inches = 600
Therefore, the value of MOA at 100 yards is 1.047 inches (0.001745 x 600 = 1.047)
At 50 yards 1/2 the 100 yard value; 70% @ 70 yards; twice @ 200 yards; 6 times @ 600 yards; and so on.
So, the difference between thinking in inches as opposed to MOA is 0.47 inch @ 1000 yards.

MOA at 500 would be 5", 600, 6" and so on.
 
Thanks for taking the time to answer my question dogpopper, that cleared that up for me! Man, there sure is a lot to shooting when u really get into it! Thanks again!
 
That kind of explanation is enough to give an old engineer, like me, chills and maybe a few little tears. Well said, Dogpopper.
 
Dogpopper's explanation is correct, but for marksmanship, MOA is generally expressed as rifleman's MOA (as he sort of referenced).

To make it easy, 1 inch equals 1 MOA at 100yds, 2 inches equals 1 MOA at 200yds, 5 inches equals 1 MOA at 500yds, etc.

It's not exactly correct, but for us it works pretty well.
 
Originally Posted By: SodakJimThat kind of explanation is enough to give an old engineer, like me, chills and maybe a few little tears. Well said, Dogpopper.
An old machinist too. Applied Trigonometry..both fascinating and sometimes frustrating.
 
Originally Posted By: huntin4emSo, is that the same for all calibers?

Nothing to do with caliber it is just a unit of measurement. Some use Minute of angle or MOA and some use mil or millradian, both are just a unit of angle.
 
Originally Posted By: huntin4emSo, is that the same for all calibers? Yes, just as 1" below the bullseye at 100 yds is the same for all calibers.
Mark
 


Write your reply...
Back
Top