Calculating MOA
- Thread starter TXAZ
- Start date
It wasn't intentional; honestly, I just don't really see that there's any significance in the fact that target rings are measured in inches given that inches is the common unit of length measurement in the U.S. that is best suited to target ring measurement.
Our measuring system uses inches so things that are roughly "inch-sized" tend to be expressed in terms of inches. That's just an artifact of the particular measurement system in use. I suppose target rings could be marked in fractions of a foot, or fractions of a yard, but that would be far more cumbersome than just marking them in inches.
If we were using the metric system, we'd probably use 3cm at 100 meters as an approximation for 1MOA and targets would have undoubtedly have scoring rings measured in cm instead of inches. None of that would establish, define or redefine the actual value 1 MOA. (Interestingly enough, 3cm at 100meters is only about 3% off the actual value--closer to the real value for 1MOA than 1" at 100 yards.)
If we used a measurement system where small lengths were measured in "blivets" that were 6 tenths of an inch and longer distances were measured in "blovets" that were 2.6 yards, then we would likely approximate 1 MOA as 2 blivets at 45 blovets (1 MOA at 45 blovets would really be about 2.042 blivets), and target rings would, no doubt, be measured in "blivets".
But 1MOA would still be 1/60th of a degree no matter what approximations we chose to employ for simplicity or what length/distance measurements we chose to use to mark target rings with.
The convention of using 1" @ 100yds is very convenient in our measurement system (I have used it and will use it again in the future), and as long as everyone understands what convention/approximation is being used, it doesn't cause any confusion. In fact, the approximation error is small enough that even if things aren't explicitly stated, the resulting errors aren't big enough to worry about in the vast majority of cases. But the idea that somehow inches/yards and MOA are linked, or that the convenient approximation explains why targets are measured in inches in a country that measures things in inches doesn't really hold up to scrutiny.
Guys, you can't use the sine of 1 moa because the sides of that angle are equal. You have to use twice the sine of ½moa to get the length ratios correct. So the actual numbers are closer to:
arc length:
1.047197547504530434637…
Chord length:
1.047197551196597746154…
Jim,
The original telescopic sights were simple telescopes with literally two hairs crossing each other in the center of the focal plane. Mount adjustments were, therefore, the only option. Internal adjustments are considered less vulnerable to external impact and jamming by mud, dirt, and grit and are waterproof, so they have pretty much replaced the external adjustments. Still, there are times I wouldn't mind having some external elevation instead of having to used fixed elevation bases to get a scope lined up for long-range.
arc length:
1.047197547504530434637…
Chord length:
1.047197551196597746154…
Jim,
The original telescopic sights were simple telescopes with literally two hairs crossing each other in the center of the focal plane. Mount adjustments were, therefore, the only option. Internal adjustments are considered less vulnerable to external impact and jamming by mud, dirt, and grit and are waterproof, so they have pretty much replaced the external adjustments. Still, there are times I wouldn't mind having some external elevation instead of having to used fixed elevation bases to get a scope lined up for long-range.
