What is MOA? Understanding Minute of Angle
Minute of Angle – or MOA – is a term which represents a measurement that is vital towards any precision rifle shooter. In fact, most rifle optics adjust their point of aim using MOA, while accuracy potential and trajectory adjustments also use this system of measurement. Minute of angle can be an overwhelming concept to grasp initially, but once properly understood, it makes things a whole lot easier. So what exactly is MOA, and how is it used in the shooter’s perspective?
Simply put, minute of angle is the term used as the standard for measuring the accuracy of a rifle, or the adjustment increments of an optic. It is an angular measurement and not a linear one, whereby 1MOA (or 1 minute) equals 1/60th of a degree. A 100 yard/meter distance is most commonly used as the standard reference to a MOA measurement, by which 1MOA is equal to a 1.047-inch diameter at 100 yards, or a 29mm diameter at 100 meters – depending on whether you use the imperial or metric system of units.
If you haven’t fully grasped the concept of MOA just yet, then you are probably a little baffled. But all hope is not lost, so bare with me as we progress through this article and try to clear things up.
Minute of Angle Explained
We’ve all heard and seen how a picture paints a thousands words, so let’s use one to try and explain the concept further.
You should know – as it is common knowledge – that there are 360 degrees in a circle. Within each degree, there are 60 minutes, giving us a total of 21,600 minutes in a full circle. One of these 21,600 minutes (as seen in the image above) is our MOA measurement, which equates to exactly 1.047 inches at 100 yards or 29mm at 100 meters. This measurement grows proportionally with range, as we can see in the image below.
As the distance from your firing point grows, so will the diameter of your MOA. This is because – as we have already mentioned – the measurement is angular and NOT linear.
At 100 yards a single MOA will be equivalent to roughly 1-inch, while at 500 yards it would be equivalent to 5-inches. At the same time, 1MOA at 10 yards would equal 1/10th of an inch, or 2.5mm.
At 100 meters a single MOA will be equivalent to roughly 30mm, while at 500 meters it would be equivalent to 150mm. At the same time, 1MOA at 10 meters would equal 3mm.
Note: the exact imperial measurement for 1MOA at 100 yards is 1.047-inches, while the exact metric measurement for 1MOA at 100 meters is 29mm. For ease of use, the figure is rounded up to 1-inch or 30mm, known as a Shooter’s MOA.
A minute of angle measurement goes on for infinity, but as a shooter, we only really concern ourselves with MOA out to distances within our rifle’s working range (or effective range). This means that we may use MOA to calculate accuracy or adjustments between let’s say 25 and 500 meters for a carbine, or 100 all the way up to 1500 meters for a long range rifle, and further in some cases.
How Does Minute of Angle Relate to Accuracy?
By understanding how a rifle and cartridge performs at 100 yards/meters, it is possible for a shooter to determine approximately what size groups the rifle will shoot within its effective range. This in turn allows the shooter to determine what size targets he can hit at a given distance, and ultimately whether a long range shot is achievable or not.
A group (or bullet hole grouping) is a series of shots – no less than 3 – fired from the same rifle, at the same point of aim, combining all principles of marksmanship to produce a pattern on the target. This pattern (or grouping) determines the rifle’s accuracy potential.
Note: when measuring the size of a grouping, the measurement must be taken using the two furthest shots or the widest spread, from the centre of each bullet hole.
A 22mm grouping (as seen in the image above) is equivalent to roughly 3/4MOA at 100 meters, therefore producing sub-MOA accuracy. Sub-MOA accuracy is defined as a rifle and bullet combination that is capable of impacting a target with multiple hits inside the diameter of a minute of angle. A half-MOA rifle should therefore achieve groupings that are smaller than the diameter of half-MOA.
Now if you have a rifle that is capable of consistently producing 1MOA groupings, and you’re wondering if your bullet would be capable of effectively impacting a 30cm steel gong at a distance of – let’s say 800 meters – then you can use your knowledge of MOA to determine the hit potential. At this distance (800 meters), 1MOA is equivalent to 240mm (30mm at 100 meters multiplied by 8), which falls well within the diameter of a 30cm (or 300mm) steel gong.
When using MOA to determine accuracy potential, your rifle needs to be tested over various distances to ensure that the MOA capability still remains. Why? We this has a lot to do with standard deviation and variation in muzzle velocities, or inconsistencies in chamber pressure. If you’d like to know more about this, read the following article: The Long Range Effects of Muzzle Velocity Variation.
The MOA Sizing Chart below shows how the grouping or measurement expands proportionally with distance.
MOA Sizing Chart (Imperial)
|Distance (yards)||MOA (inches)||SMOA (inches)|
MOA Sizing Chart (Metric)
|Distance (meters)||MOA (mm)||SMOA (mm)|
How Does Minute of Angle Relate to Scopes & Optics?
When it comes to rifle scopes and optics, MOA is one of two measurement systems used to adjust the scope turrets in order to zero the rifle and compensate for bullet drop and wind drift. The other measurement that can be found is known as MRad (or Milliradian). If you’d like to know more about MRad, you can read the following article: Mil vs. MOA – What’s the Difference?
Turrets commonly adjust in increments of 1MOA, 1/2MOA, 1/4MOA, and in some cases even 1/8MOA. A 1/4MOA turret will require 4-clicks to move the bullet impact 1 full minute of angle. This means that 4-clicks of an elevation turret will move a bullet’s point of impact 1-inch vertically at a distance of 100 yards.
I know that this concept can take some time to grasp, so until you understand how MOA works for both accuracy and scope adjustments, you can refer to the scope adjustment charts below when making adjustments to your zero.
|Increments||25 Yards||100 Yards|
|Increments||25 Meters||100 Meters|
However, if you’re using MOA to account for bullet drop, wind drift, and various other external ballistic factors, then you’ll most likely need a good understanding of how MOA works before you’re able to progress through your long range shooting.
While the concept of MOA may be difficult to grasp initially, it does simplify with practice. Further online research along with practical application will go a long way in understanding the minute of angle and how it relates to both scopes and groupings/ precision over various distances. So keep practicing and you will soon take to the concept of MOA and precision DOPE adjustments.
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