Precision Fundamentals

If you are an American shooting enthusiast, chances are you have heard the term “MOA”. Minutes of  angle/arc (or MOA) was the most common unit of measurement utilized by American market riflescopes to adjust point of aim prior to 2005. Around that time a “new” adjustment system started making its way to American market rifle scopes: mils. Mils (or MRAD) is an abbreviation for milliradian. But before we dive into the weeds of the differences between these two units of measurement, let’s refresh our minds with the basics of riflescope operations.

A modern riflescope is designed to give the shooter a definitive and repeatable point of aim (POA). The optic itself does not mechanically move the rifle it is attached to; it is simply a reference point for the shooter to utilize when physically changing the orientation of the barrel. There are two basic designs of riflescopes regarding adjustments: those with turrets designed to be set during the “zeroing” process and then subsequently left alone, and those designed to be manipulated during use.

Those shooters using the first mentioned design are most likely used to thinking about the “click” value of their scope’s turrets in relation to adjusting their POA to their point of impact (POI). Once POA/POI has been achieved, cover caps are replaced and Kentucky windage is in effect. Shooters using the latter design have the ability to make adjustments at different ranges in differing external conditions while always holding the reticle at a consistent aiming point. Either way, having a better understanding of how the adjustments made on the rifle scope will translate to shot placement is always advantageous.

The Minute of Angle/Arc

MOA is simply an angular unit of measurement – just like a degree. Most of us learned that there are 360 degrees in a circle at a young age. A degree is a relatively small unit of measurement for the majority of our daily life interactions; therefore, most don’t have a need to break a degree down into a smaller unit. But a degree can be too large for precision tasks, like riflescope adjustments, so a degree can be divided into 60 equal parts. 1/60^th of a degree is known as a minute – or MOA. Why do riflescopes utilize this type of measurement unit? Because angles remain relative to distance. An inch is an inch whether you are referencing 100 or 1000 yards away. An angle such as a MOA has a different “size” value depending on the point referenced along its path. A one MOA shift is equal to 1.047” of shift 100 yards away but equates to 10.470” of shift at 1000 yards for the very same adjustment.

Picture your shooting position at the center of a circle. Every left or right adjustment you make with the windage turret moves your POA a fraction of a degree. Depending on how far away from your position (center of the circle) you reference, correlates to a larger amount of shift each adjustment makes. This shift is reduced the closer you move back to the center (your position) and increased the further away you move from center. Same applies to vertical adjustments made with the elevation turret. Picture your position center of a circle as if the circle were passing over your head and then beneath you. Elevation adjustments follow a vertically aligned arc. Next time you look at a riflescope crosshair or reticle, picture the two-dimensional vertical and horizontal lines as the edges of two circles bisecting one another in three-dimensional space.

The Milliradian / Mil / MRAD

Just as a MOA is nothing more than an angular unit of measurement (a smaller degree), such is also the case for the milliradian. The base difference is that mils is a derivative of the metric (SI) system. To understand the scale of a milliradian, we must first look at the radian of which the milliradian is derived from.

A radian is an angle or arc just as a degree, albeit much larger. To find the radian of a circle you will start from the center and draw a straight line to the outside edge (the circle’s radius). From there you will trace a portion of the circle’s circumference the equivalent of the radius. From where you ended, come back to center with another straight line (another radius). The resulting “pizza slice” where the two edges (radiuses) are equal in length to the “crust” (portion of circumference equal to radius) is the circle’s radian:

There are 6.283 radians per circle. Radians are based on Pi (every circle has 2 Pi radians) and Pi is an irrational number (the numbers following the decimal will continue forever in a non-repeating fashion), therefore we will need to round off Pi (3.1415926535….) to a usable number. For the purposes of determining the value of a milliradian we will “stop” Pi at 3.1415 – and since there are 2 Pi radians per circle, we will double this number and end with 6.283 radians per circle.

As there are 360 degrees per circle that can be divided into smaller units of measurement, so there are 6.283 radians per circle that can also be broken down into smaller units of measurement. Just as a millimeter is one thousandth of a meter, a milliradian is simply one thousandth of a radian. Therefore, it can be deduced that there are 6,283 milliradians per circle.

But wait – my military family have been told there are 6,400 mils per circle. Whether for land navigation utilizing a compass to shoot an azimuth, or correcting indirect fire utilizing a mil scale, the standard U.S. military circle utilizes 6,400 mils rather than the mathematically correct 6,283 number. Why? Great question – if anyone out there knows I would love to pick your brain. And don’t bother trying to convince me that it has to do with even numbers that are easier to work with – 6,200 is an even number that is much closer to being correct.

So, which is better?

 To answer this very common question, we are better suited to establish some relevant standards in which to compare these two angular units of measurement by. For the purpose of brevity and practical simplicity, we will limit these standards to size, ease of use, and commonality.

 Size:

A MOA is a smaller unit than a MRAD, however, this statement is somewhat misleading. Most MOA scopes turrets are calibrated to move your POA .5 or .25 MOA, whereas most MRAD turrets move your POA .1 mil. A tenth (.1) of a mil is a smaller (finer) adjustment than a half (.5) MOA, but larger (courser) adjustment than a quarter (.25) MOA. Advantage of a finer unit of adjustment: you are able to really fine tune your POA such as when zeroing the rifle to better match your intended POI. Example: I am aiming at a 1” circle at 100 yards. My impacts are inside the left side of the circle. If my scope adjustments are in .5 MOA increments, then the smallest adjustment I can make will put my impacts to the inside right side of the circle. A .25 MOA adjustment, however, would get you closer to center. Disadvantage of a finer unit of adjustment: smaller internal parts are more susceptible to damage or slippage when a grabbing a handful of turns when bold adjustments are needed. Conclusion: if you are shooting bench rest and looking for exceptionally fine adjustments, .25 MOA or smaller (.125 or even .0625) is what you should be looking at. If you are a hunter that uses drag bags as their namesake suggests, or looking to repeatedly dial your elevation every shot, .1 MRAD might be the sweet-spot way to go.

 Ease of use:

Most shooters who are familiar with MOA reference 1 MOA being equivalent to 1 inch at 100 yards. Example: I move my turret up/down/left/right 1 MOA (2 “clicks” if turrets are calibrated in .5 increments, 4 clicks if .25, etc.) and my impact will shift 1 inch on a target 100 yards away in the direction chosen. At a distance of 200 yards, that same 1 MOA adjustment would move my impact 2 inches, 3 inches at 300 yards, and so on. This is a close reference, but not mathematically accurate. One MOA of adjustment will move your impact 1.047” at 100 yards. Practically speaking, .047 of an inch is a difference of less than a half inch at 1000 yards, so depending on what level of accuracy you are trying to achieve this may or may not be an issue.

 If you are using a scope with MRAD adjustments, then 1 MRAD is equal to 10 centimeters at 100 meters (or 1 centimeter if you adjust .1 MRAD). This lends itself to mathematically rounded numbers, however, this only applies when you shoot in meters rather than yards as there are 1.094 yards per meter. This .094 yard difference becomes harder to ignore when there is almost a 100 yard difference between 1000 meters and 1000 yards. Who in the U.S. actually shoots small arms in meters? Not the Marine Corps. Everything else in the military is referenced in meters – artillery, distance, max effective ranges of weaponry; but service rifles such as the M4 or M40 are zeroed and shot in yards. I know, this doesn’t make sense to me either.

 So, based on inches/yards being referenced with MOA and centimeters/meters the reference for MRAD, Americans used to inches and yards seem to benefit the most utilizing MOA in terms of ease of use, right? Maybe. If you are using a riflescope that has capped turrets intended for zeroing only and a reticle with little to no reference points, you may find it easier to “eyeball” your adjustments when thinking in inches. But, if absolute accuracy is the goal, you should be utilizing a measuring apparatus such as a reticle with defined reference points to make your adjustments. If your optic has a MRAD reticle (riflescope or spotting scope), you can overlap this reticle on your target and measure the exact distance in MRADs that you need to adjust. Measure, dial, fire – no guessing, no math. This also applies to a MOA optic with a MOA reticle. Keep in mind that if the optic has variable magnification (zoom) then the reticle scale will only be correctly calibrated if the optic is either a front/first focal plane (reticle remains relative to target size throughout the magnification range), or a second focal plane that is at its highest magnification setting (almost always the case). If you happen across an optic that mixes the two together (MRAD reticle with MOA turrets) then you will need to convert your readings before adjusting (there are 3.438 MOA per MRAD) or burn it with fire (preferred). This mash-up between the two angular units of measurement is very rare in commercially available modern riflescopes and most will never have to consider this scenario (shoutout to my 8541 spanner-wrench brothers!).

 Commonality:

There was a time not long ago when MOA ruled the American market landscape and MRAD was nothing but a tale whispered of the European lands. This is no longer the case. Why the change? I believe this is directly related to the USMC sniper program changing to a MRAD riflescope, but since there is no way for me to confirm this, I will leave it as opinion. There are many riflescope manufacturers today offering identical models with either MOA/MOA (turrets/reticle) or MRAD/MRAD units. I still notice a trend of some manufacturer’s American market hunting-style riflescopes (commonly capped turrets used only for zeroing) offered primarily in MOA, and even fewer cases of “tactical” style models offered exclusively in MRAD, but there are no shortages of quality riflescopes offered in your choice of angular unit of measurement.

Winner:

You. There is no universal advantage that either the MOA or MRAD system possesses that applies to every shooter in every discipline. Take an inventory of your specific goals and preferences and compare them to the synopsis above. At its essence, MOA and MRAD are two approaches to the same task using different but equally effective solutions to achieve the same results. Having a clear understanding of how each system works will make you bilingual in the modern riflescope sphere and allow you to expand your purchasing and operating options. The American shooting enthusiast is the winner of this contest as there is nothing more American than choice.