If you’ve spent any time on a rifle range, read the descriptions of guns and optics online, in catalogs or in magazines, or heard people in a gun store talking about how good this or that gun or scope is, you’ve probably seen or heard the term “minute of angle” or “MOA.” Just what the heck is that?
In its most basic form, MOA is an expression of accuracy. The cool thing about it is that once you can understand what it is, you can quickly and easily adjust your scope so you can aim at the center of the target at 100 yards as easily as 200, 300, 400, 500 yards and beyond. The limitations to its usefulness depend on the ballistics of your rifle and bullet, environmental conditions and your own abilities. Before we get to those limitations, though, let’s talk about the specifics of MOA.
Just What the Heck is MOA?
Though we’re applying it here to rifle accuracy, “minute” is just a fancy word for 1/60. Just as it is with time, there are 60 minutes in one hour. Each minute is, therefore, 1/60 of hour. But how does this apply to rifle accuracy?
When discussing MOA, we typically depict 1 MOA as an “impact difference” of one inch at 100 yards. To be really specific, the actual measurement is 1.047 inches, but at 100 yards the .047-inch is so minimal we simply round it off to one inch for practical use.
What do I mean by “impact difference?” When a rifle is fired, the bullet leaves the rifle at an angle, following an arc until it contacts its target or, eventually, the earth. To hit your target at varying distances, you adjust your scope (or iron sights, but we’re going to stick to scopes for this discussion) accordingly, but what you’re really doing with those adjustments is changing the angle of elevation of the rifle.
An example. Let’s say your bullets are consistently impacting the target about one-inch low from your intended impact at 100 yards. To compensate, you would not change the rifle’s elevation by one inch, rather you would change the position of the reticle in the scope by the required amount. I’ll get to how to do that shortly, but let’s talk a minute about why understanding MOA is important in the first place.
Why is MOA important?
Many different forces will affect your bullet’s flight. These can include, but are not limited to, your primer, powder type and powder burn rate, plus environmental factors such as wind, humidity, air density and gravity and even the rotation of the earth. Of the environmental factors, gravity has probably the greatest affect on bullet travel. Fortunately, gravity is constant, which makes it the easiest to compensate for. To do this, we use MOA.
To understand gravity’s effect, consider this. Once fired, the bullet immediately begins to slow due to wind drag and other environmental factors. Therefore, the first 100-yard increment would be travelled fastest and each incremental 100 yards after would be slower than the previous 100-yard increment. Because the bullet takes longer to travel from 300 to 400 yards than it did from 0 to 100 yards, it is subjected to gravity for a longer period of time, which equates to more bullet drop. Therefore, to be accurate at longer distances, you must compensate accordingly to reach the desired impact point at any given distance, and you use that by employing MOA.
Using MOA to Move Your Group
There’s one more basic fact you need to understand about MOA before you put it to use. So far I’ve mostly talked about 1 MOA being about one inch at 100 yards. But what is it beyond that yardage? The best way I can think of to understand MOA at distance is to think of a laser pointer run through the barrel of your rifle. If you began with the laser dot on the center of the X-ring of a target standing at 100 yards and the barrel angle was increased 1 MOA, the dot would then be about one inch high at 100 yards. At 200 yards that laser dot would be two inches high, and it would be three inches high at 300 yards and so on. See how the increment of change kind of matches the yardage? What this boils down to is that two inches high at 200 yards and three inches high at 300 yards means a rifle is still shooting 1 MOA at each of those yardages. I know, a little hard to wrap your head around that, so take my word for it, it’s easier if you just memorize that and take it for what it is instead of trying to do mathematical gymnastics all day long.
Using MOA to Move Your Group
As I first told you, it’s adjustments to your scope that causes you to effectively change the angle of your barrel to the target and move where your shot impacts. To do this, you’ll use the scopes “turrets,” the knobs on the top and side of the scope body. The top turret adjusts for elevation (up and down movement), while the side turret adjusts for windage (left and right movement). The turrets are designed to move the reticle in certain clearly defined increments. The majority of scopes have turrets set for ¼-MOA clicks, meaning four “clicks”—you can generally feel the stop or “click” of each increment as you slowly turn the turret, or it will have fine hash marks on the face of the turret itself that indicate visually how far you’ve turned it—to equal 1 MOA or one inch. Other scopes have clicks set at 1/8 and even ½ or 1 MOA.
This is what a typical scope turret looks like. You’re scope will have one on top to adjust elevation (up and down movement of the reticle) and one on the side for windage (left and right reticle adjustment).
Using a scope that has ¼-MOA clicks as an example, let’s say you have a rifle that has the scope “zeroed” at 100 yards. “Zeroed” means that when the crosshair of the scope is centered on the target, the bullet will impact that exact spot at 100 yards. you’re shooting two inches low of where you want your group to be. Since it takes four ¼-clicks to make an inch, you would need to make eight clicks to move your group two inches. You would do this with the topside turret—the one for elevation. This turret should be marked on its face with “Up” and “Down” or “U” and “D” and with arrows indicating which turning direction will produce the desired result. So, for the two-inch low group, you’ll turn the turret dial of a ¼-MOA regulated scope eight clicks in the direction of the “Up” indication because that’s the way you want your group to move.
It’s worth looking at this in a slightly different way. Using that same rifle zeroed at 100 yards, let’s say that you want to do most of your shooting at 200 yards, but after a couple groups at that distance, you see those groups are impacting four inches low from where you held the crosshairs centered on the target. Recall that 1 MOA equals both one inch of movement at 100 yards and two inches of movement at 200 yards. Knowing that, you would then adjust 2 MOA to compensate for the four inches of difference between where your crosshairs were centered and where you want your actual impact point to be (1 MOA= 2inches at 200 yards; 2 MOA x 2 needed inches of movement = 4 inches of drop).
There’s still one more example I need to provide you, and this one has to do with the effect of gravity I spoke about earlier. As I explained, a bullet slows in its travel over time, giving gravity a greater effect as the distance the bullet travel increases. Let’s assume that while the bullet dropped four inches between 100 and 200 yards, it then dropped 15 inches by the time it reached the 300-yard mark, 32 inches at the 400-yard mark and 60 inches at 500 yards. We know that 1 MOA at 300 yards equals three inches. Therefore, we would need to aim 5 MOA high (3×5=15) to hit the center of a 300-yard target. Continuing with our example at 500 yards, I stated there would be 60 inches of drop. One MOA at 500 yard equals about five inches. Therefore, we would need 12 MOA or 12 of the five-inch units (12×5=60) to compensate for the difference between our aim point (center of the target) and our impact point (60 inches below the center of the target).
Beyond the Math
So that’s the math, but what does it mean in practical application? By shooting a group and then moving that group via MOA increments in your scope, you can then keep the crosshairs of that scope on the place you want your bullets to impact. Without that, you’d have to hover the center of the crosshairs above, below or to the left or right of where you wanted to hit and hold it in that estimated position to make the shot—and why guess at it when the scope and MOA can do the work for you?
Most rifle ammunition boxes today come with ballistics information, or how that particular loading is expected to perform at certain yardages. You’ll need this information to refine your use of MOA.
It really can be that easy to compensate for range. Remember MOA and learn your rifle’s “ballistics” for your intended load. Ballistics data—expected drop at certain yardages and other bullet travel information—can be obtained from many cartridge boxes, ballistics or reloading manuals, or manufacturer websites. You’ll need that information to work in conjunction with what you’ve learned here about MOA. However, this will only be a starting point of improving your shooting skills over distance—because nothing beats time spent at the range to determine the actual performance from your rifle and ability.