He’s shooting minute of angle, they say knowingly. The rest of us just stare blankly. If you’ve ever read any novels or seen any movies about snipers or expert marksmen or military heroes, you’ve no doubt met a character who shoots minute of angle (MOA). Writers throw this term around like we were all born knowing what it means, and they rarely give a good explanation for it. Well just in case it comes up in conversation next time you’re talking to a gun enthusiast, here’s what you need to know.

First of all, minute of angle is a measurement, and it’s not limited to shooting. The minute part refers to the fact that one angle degree, like one hour, is divided into 60 minutes and further into 60 seconds. So a minute of an angle is 1/60 of a degree. This is also true for degrees of latitude and longitude, which are divided into minutes and seconds representing actual distances on earth. In fact, the distance covered by one minute of latitude at sea is the definition of a nautical mile or knot, but that’s another chapter (see the chapter cleverly titled “Why Knot?”).

So how on earth does this apply to shooting a rifle? Easy. Imagine you’re shooting at the bullseye on a target. The closer your bullets are to each other (and to the bullseye), the better you’re shooting. After you’ve fired all your rounds, leave your rifle exactly where you shot it from and locate the two holes on the target that are the farthest apart. Now draw an imaginary line from each hole to the business end of the rifle’s barrel. You’ve now created an imaginary angle at the rifle’s barrel, i.e. the angle between the two lines. The smaller that angle, the more accurately you’re shooting (if all your bullets when into the same hole, the angle would be zero). If the angle is less than or equal to one minute of one degree, then you’re shooting one MOA or simply, you’re shooting minute of angle.

But fortunately you don’t need to actually draw the lines to your rifle, because this problem was solved long ago. If you measure the distance between the two bullet holes, and the distance between your rifle and the target, you can use simple trigonometry to calculate the measurement of the angle. It turns out that at 100 yards, a one inch distance between holdes is very close to one MOA, so this has become the rule of thumb: if your holes are one inch apart at 100 yards, you’re shooting minute of angle. Similarly, at 200 yards a distance of two inches is also one MOA, just as at 300 yards a distance of three inches is one MOA, and so on. The farther away the target, the more distance you’re allowed between holes to be considered minute of angle. So if you’re shooting at a target 500 yards away and put all of your bullets in a group with a maximum distances less than five inches (this would be called a five-inch group), you’re shooting minute of angle at 500 yards, which we can all agree is pretty good. Even if you’re not shooting minute of angle, you can still classify your accuracy in terms of MOA: at 100 yards a two-inch group is two MOA, a three-inch group is three MOA, and so on.

So, knowing all this, how do you learn to shoot minute of angle? Practice, practice, practice.