The Firing Line Forums - View Single Post - I'm looking for a technical definition of MOA

Vek · January 30, 2001, 02:57 PM

Somebody said this before, but we'll try again...

There are 360 degrees in a circle. Another more useful form of angular measure is the radian. There are 2*pi radians in a circle, or 180 degrees is pi (3.1416) radians. A minute of a degree is 1/60 of a degree. Or, if you're really nerdy, 1/60 degrees times 3.1416 radians/180 degrees gives .0002909 radians. "my rifle shoots .0002909 radians".

The fun thing about the radian is that one can get arclength simply by multiplying angle measure in radians times the radius of the arc. For example, everybody knows that the circumference of a circle is 2*pi*radius or pi*diameter. 360 degrees is 2*pi radians, or 6.2832 radians. multiply 6.2832 by the radius of the circle and you get the circumference (arclength of 360 degree angle).

Take a circle 600 feet in diameter (100 yard radius). 0.0002909 radians times 300 feet times 12 inches/foot gives 1.0472 inches for the arclength of 1/60 degree at 100 yards. Somebody also had a concern about this arc not being a straight-line measurement. Get yourself 100 yards of spectra fishing line, tie it to a post, go out 100 yards and tie a pencil to the string. use the pencil to draw a 1" long arc, and see how much it varies from a straight line.

Did this help?

January 30, 2001, 02:57 PM	#22
Vek Member Join Date: May 22, 2000 Location: Bellingham, WA Posts: 48	Bear with me... Somebody said this before, but we'll try again... There are 360 degrees in a circle. Another more useful form of angular measure is the radian. There are 2pi radians in a circle, or 180 degrees is pi (3.1416) radians. A minute of a degree is 1/60 of a degree. Or, if you're really nerdy, 1/60 degrees times 3.1416 radians/180 degrees gives .0002909 radians. "my rifle shoots .0002909 radians". The fun thing about the radian is that one can get arclength simply by multiplying angle measure in radians times the radius of the arc. For example, everybody knows that the circumference of a circle is 2piradius or pidiameter. 360 degrees is 2*pi radians, or 6.2832 radians. multiply 6.2832 by the radius of the circle and you get the circumference (arclength of 360 degree angle). Take a circle 600 feet in diameter (100 yard radius). 0.0002909 radians times 300 feet times 12 inches/foot gives 1.0472 inches for the arclength of 1/60 degree at 100 yards. Somebody also had a concern about this arc not being a straight-line measurement. Get yourself 100 yards of spectra fishing line, tie it to a post, go out 100 yards and tie a pencil to the string. use the pencil to draw a 1" long arc, and see how much it varies from a straight line. Did this help?