Dumb question about MOA...

[Molon Labe]

I understand what a minute of angle (MOA) is. And I understand that, at 100 yards, 1 MOA is approximately 1 inch, 2 MOA is approximately 2 inches, etc.

But when someone says they "shot a 2 MOA group at 100 yards," for example, are they saying they shot a circular group with a radius of 2 inches or a diameter of 2 inches?

I believe the correct answer is "diameter." But why is that? Why isn't it radius?

Let's say I'm aiming for the bulls eye, and all my shots are scattered around the bulls eye. My maximum error is the hole farthest away from the bulls eye, correct? If that's true, shouldn't MOA error be defined in terms of radius instead of diameter?

 

[duckslayer]

They are referring to the spread between the farthest two holes on the target, not the distance of any particular shot from the bull's eye.

 

[Flyboy]

It's not referring to the error, it's referring to the group size. That is, the total distribution of rounds covered 2 minutes of arc.

 

[bjbarron]

Flyboy is right.

Don't think circles (radius and diameters) think triangles or cones.

Your cone has long 100yd sides and one short 2" diameter circular base at the other end. You goal is to shoot from the apex of the long sides and keep your shots within the enclosed area of the cones base at the other end. Then you are shooting 'within 2 Minutes of Angle'...even if it appears to be a circular distribution.

 

[Joejojoba111]

Molon Labe, I think I think like you. When I read your post I agreed, 'why don't they?'. But now I think about it some more they probably use the diameter because you have no control which side of the bullseye your shot will fall on. It might be the left, might be the right, so you have to go with diameter instead of radius.

 

[Molon Labe]

Molon Labe, I think I think like you. When I read your post I agreed, 'why don't they?'. But now I think about it some more they probably use the diameter because you have no control which side of the bullseye your shot will fall on. It might be the left, might be the right, so you have to go with diameter instead of radius.

I was confused because I thought shooters used "MOA" to refer shot placement error. While they certainly could define it this way, apparently someone long ago decided that "MOA" is a measurement of maximum spread, not error.

In a nutshell… the "tightness" of a group can be defined in terms of maximum MOA error (a.k.a. accuracy) or maximum MOA spread (a.k.a precision). Shooters apparently value precision over accuracy, thus the latter definition is used.

 

[hksw]

Shooters apparently value precision over accuracy,...

For most of us, yup.

Easy to correct accuracy, just move the sights/crosshair. Not so easy to attain precision.

 

[ceetee]

In talking about "error", you seem to say that your rifle is only capable of shooting in a perfect line... that is, if you locked the rifle in a vise and fired it at a target 100 yards away, all bullets fired would go through the same hole. Don't we wish!

There are plenty of variables (wind, thermal updrafts, barrel harmonics, inconsistant powder loads, etc.) that affect the bullets flight.

Accuracy, then, is the combined total of how well the rifle shoots, plus (or minus,if you prefer) how well the shooter shoots that particular rifle...

 

[Keitha]

Minute of angle (MOA) is a geometric term, not firearm specific. A circle is 360 degrees, each degree has 60 minutes, and each minute has 60 seconds. So 1MOA is 1/60 or a degree.
Now think about the "cone" example that bjbarron gave. The base of the cone (on the target) gets larger as you move further away. An analogy would be a flashlight; close up it has a narrow beam but further away the beam area gets larger. 1MOA equates to about 1" at 100 yards or 2" at 200 yards etc.
All they are saying is that the gun should be able to consistently shoot within the cone base area (which would look like a 1" circle at 100 yards for 1MOA).

 

[bogie]

Say you've got four shots in a little cluster. Then you get stupid, and lose one when the wind switches.

Measure from where the paper is, to where the paper is. Subtract one bullet diameter.

That's your group size.

A 2MOA group at 200 yards if 4".

A 1 MOA group at 200 yards is 2"

A 1 MOA group at 1,000 yards every time, all day long, with his trust Ruger Mini-14, is the figment of the imagination of a fellow who commonly wears hawaiian shirts...