rifle, sight, accuracy, precision-rifle, terminologyWhat does Minute of Angle (MOA) really mean and how is it applied to marksmanship and firearms?
I understand that it has something to do with the arc that the bullet travels but beyond that I don’t quite get it.
As others have explained an MOA is an angular measurement.
Why is an angular measurement useful?
The aiming errors we make at shooters are basically angular errors. Say a shooter is steady enough aiming and trigger control to break our shots within (say) a 3” circle at 100 yards. Obviously if he is aiming at a target at 20 yards he’ll be breaking his shots inside a circle 1/5th the size (since 20 yards is 5 times closer than 100 yards). And if he is aiming at a target 300 yards away, he’ll be breaking his shots inside a circle 3 times as large (because 300 yards is 3 times as far as 100 yards). But in all cases, he is breaking his shots inside a 3 MOA circle, which is why it is much more convenient to describe the accuracy of a shooter in terms of MOA rather than in inches (because “inches” alone isn’t enough, it always has to be paired with the distance too).
Now as why MOA and why not other angular units (such as mils, or decimal degrees)? A few reasons:
when measuring distances in yards and bullet locations in inches, an MOA is so close to being “an inch per hundred yards” that it is too convenient to ignore
some rifles are more accurate that one MOA and some are less, but one MOA is a pretty conveniently-sized measuring stick for rifle accuracy. One MOA is pretty darn good for a factory rifle; 2-3 MOA is acceptable accuracy for most factory rifles; just about any half-shot-out rifle ought to be able to deliver 5 MOA; a half-MOA rifle is really quite something; a quarter-MOA rifle is a level that most competitive target rifles don’t achieve.
also, one MOA is a usefully-sized measuring stick for shooter accuracy too (when firing prone with iron sights shooting jacket and sling, an intermediate-level shooter will put the vast majority of his shots into a 2-MOA circle; best-in-the-world level shooters can put ten out of ten shots into a 1-MOA circle but this is hard enough that they will savour it!)
For what it’s worth the next most common angular measurement you will find is the “mil”, which is one part per thousand (the mil is bigger than the MOA, in rough terms a mil is about three MOA).
Minute of angle is the measurement of a round’s deviation from its target. The exact measure of MOA is 1.0471996” at 100 yards. It is often rounded to 1” exactly for the sake of making math easier.
For example: if you fire two shots at the center of a target from a distance of 100 yards, and your shots are 1” apart, you have shot a 1 MOA group. If you shot the same group (2 shots in 1”) at twice the distance (200 yards), it’s half the MOA (1/2 MOA). Half the distance (50 yards) is twice the MOA (1” at 50 yards = 2 MOA). 3 times the distance, 1/3 the MOA (1” at 300 yards = 1/3 MOA), etc.
MOA is often used to indicate the accuracy of a shooter or of equipment. Saying that a rifle will “shoot sub-1-MOA groups” generally means that given ideal circumstances (like placing the rifle in a rest) it will repeatedly shoot inside 1” at 100 yards, 2” at 200 yards, etc. They use this to indicate that the rifle is accurate, and if it isn’t performing well the problem is you, not the rifle. In the context of a shooter, people often say “I’m a half-minute shooter on a good day,” or similar, to mean that given a rifle that’s capable of .5 MOA (half inch at 100 yards, 1 inch at 200 yards, etc.) they can accomplish that level of accuracy.
A Minute of Angle is one sixtieth of a degree (just like a minute is 1/60th of an hour). A minute of angle covers approximately one inch at 100 yards (1.047 inches to be more precise). It is used in several contexts related to firearms.
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