- Types of mil-dot reticles
- USMC Mil-Dot
- US Army Mil-Dot
- Mil Relation Formulas
- Other uses of the mil-dot reticle
Ah, the wonderful mil-dots! The reticle that defined tactical shooting decades ago, and is around even today. There are many new reticles that were created to improve upon the original, but there is still something charming about the clean and easy to use mil-dot reticle. Everyone has seen them, and even today they just look so cool. But alas! There is more purpose to the mil-dots than just looking good. The millradian was developed by the artillery a number of years ago and has been used to adjust fire for a lot longer than snipers have been using them to estimate range. A millradian is 1/6283.2th of a circle, or 3.438 MOA (most people round to 3.44) Now, I’m not going to get into the details of where those numbers come from, but it can all be figured using common math. More importantly to us, is that a millradian represents 1 unit of measure at 1000 units of measure. The units of measure do not matter as long as they are the same. So, to simplify, if a 1 yard tall target was 1000 yards away from you, it would measure 1 millradian. Lets carry it one step further, if you were looking through a scope with mil-dots, at a 1 yard tall target, and you measured it to be 2 mils tall. Knowing that it would measure 1 mil tall if it was at 1000 yards, you would easily determine the range to be 500 yards since the measured height was twice as tall as 1 mil, it would make sense that it was twice as close, or half the distance, 500 yards. That is the basic concept of mil-dots, which are just to measure millradians. (mil being short for millradian). Now, we can talk about it in more detail.
Types of mil-dot reticles
In the beginning, the USMC is responsible for
bringing the use of millradians to snipers, at least in the USA. I am not sure
when their use was adopted by other countries around the world. The USMC put
the mil-dot reticule in their Unertl USMC scopes, which were adopted in the
early 80’s. This reticule is known as the 3/4 USMC Mil-dot. The reason is
because each dot is 1/4 of a millradian in diameter and that leaves 3/4 of a
mil between each dot. One VERY important note to be made is that the distance
from center to center of the dots is 1 millradian. Now, because we know the
exact size of the dots, one can measure the size of their targets accurately.
The USMC reticle is easy to break down into 1/8 increments because of the 1/4
(2/8) size of the dots. It is imperative that you measure the target as
accurately as possible. When you are measuring targets a long ways away, every
.1 millradians off you measure your target is huge. In example, if you are
mil-ing a 6 foot tall target at 1000 yards and you are off by just .1 in your
millradian measuring, your range estimation will be off about 50 yards, enough
for a clean miss at those ranges. You must be accurate. So, here is a quick
break down of the USMC mil-dot measurements.
Now, in the later 1980’s the US Army was looking to field their new sniper rifle, the M24, and part of the requirements was a mil-dot scope. Their mil-dots ended up being different than the USMC 3/4 mil-dot reticule. The Army mil-dots are .75 MOA, which equates to .22 mils, these are smaller than the USMC dots. When using the Army dots, the dots are generally rounded to being .2 Mil long, which makes its use for measuring very handy. It becomes very easy to break down the measuring into .1 increments. Unfortunately, getting much more accurate than .1 is very difficult, and usually not worth the effort. Of course, the distance from center to center of each dot is still 1 millradian. Is the Army version better than the USMC 3/4 Mil-dot? That is totally an opinion of the user. Each has its advantages and disadvantages. Here is a diagram in more detail of the US Army mildot reticule.
US Army Mil-Dot
These are the two main mil-dot reticules out there, but there are many others. In fact, just about every scope manufacturer that builds a mil-dot scope has a slightly different mil-dot reticule. The important thing to remember is that you will need to get very familiar with whatever millradian reticule you are using. It is extremely important to know all the minor measurements on the reticule, this allows you to make much more precise measuring of the target. One thing to be careful of with illuminated mil-dot reticules is that if you have the brightness turned up too high it can make the reticule “appear” larger, possibly throwing of your millradian measurements. If you using an illuminated mil-dot reticule, be sure to turn the intensity setting to only as high as is necessary.
Mil Relation Formulas
Well, we know how to measure a target using mil-dots now, but how do we determine the range to the target? Here is where we get into the math portion of this, and is also why we carry calculators into the field. The basic mil relation formula goes like this:
Size of target (units of measure)
———————————————————– X 1000 = Range (units of measure)
Size of target (mils)
So, lets take a quick example. Lets say we are scanning over a clearing, and out walks a 2 yard tall terrorist. Now, since we know the size of the target in yards, that will be our “units of measure”. Now, we quickly, and accurately mil him at 3.4 mils tall. We can plug our data into our formula and get this:
—————– X 1000 = 588 yards
Okay, so our target is 588 yards away. Pretty simple eh? But can we make it more simple? Of course we can! The first thing we can do is switch up the units of measure a little. Not many people would be able to tell if a guy is 1.88 yards tall, but they WOULD be able to tell if he is 5’8″, or 68″ tall. So, the formula would be a bit more useful if the unit of measuring the target was in inches but the unit of the range to the target was still in yards. Well, using a little bit of basic algebra will get our formula to do just that!
We known that for every yard, there are 36 inches. So, we can substitute in our 36 inches per yard and start simplifying. Also, keep in mind that the 1000 constant can also be written as 1000/1 which will allow us to write our formula out like this
Size of target (yards) X (1 yards) X 1000
————————————————————- = Distance (Yards)
Size of target (mils) X (36 inches) X 1
Now, the one obvious reduction is deviding the 36 into the 1000, and then we come up with our new standard formula.
Size of target (inches) X 27.78
—————————————————– = Range (Yards)
Size of target (mils)
If you are dealing in yards, and know inches well, this is the formula to use. Go ahead and try it with the example above to be sure you get the same numbers.
Now, for the USMC and most of the USA, the yards are fine. And of course, if you are using the metric system, its a piece of cake, because its purely 10 based. Just take the normal mil-relation formula and use meters as your units of measure. If you would like to estimate your target size in decimeters, or centimeters, you would just have to reduce the 1000 constant by the proper number of 0’s. In example:
Size of target (centimeters) X 10
———————————————— = range (meters)
Size of target (mils)
Now, what if you are like the US Army, and do everything in meters, but really are familiar with estimating target size in inches? Not to worry. With some more basic algebra we can come up with a formula that allows to use target size in inches and get the distance in meters. So, we can take our basic forumla and use meters as our unit of measure since we want our range in meters. We also know that the conversion between meters and yards is .9144 meters per yard, so we’ll multiply our meters unit by .9144. We’ll also use the 1000/1 representation of the 1000 constant to help us simplify our formula. So we get this for a formula:
Size of target (meters) X (.9144 yards) X 1000
———————————————————————– = range (meters)
Size of target (mils) X (1 meter) X 1
Okay, now lets simplify all that by multiplying the numbers out. We also want to measure our target in inches, and not yards, so lets convert to inches by dividing by 36 since there is 36″ per yard.
Size of target (yards) X 914.4
———————————————————– = range (meters)
Size of target (mils) X (36 inches)
Okay, all we have to do now is divide that 36 into the 914.4 and we come up with our new wizbang formula for measuring our target in inches yet get our range in meters… and here it is in all its glory!
Size of target (inches) X 25.4
————————————————– = Range (Meters)
Size of target (mils)
And that is the formula that is used by most US Army snipers. Now, there is one other formula that is used by a few law enforcement sharpshooters that works very quick, but you have to be able to estimate size in centimeters. It goes like this: estimate how many centimeters 1 mil covers on the target, add a zero to it, and you have the range to the target in meters. For instance, if one mil covers 15 centimeters (about 5.9″) on the target, then the target is 150 meters away (just put a zero on the end of the 15 centimeters). Its very fast and easy if you can estimate centimeters. Well, that concludes our portion on the mil-relation formula, I hope I didn’t completely confuse everyone.
Other uses of the mil-dot reticle
Now, we have discussed how we use the mil-dots to estimate range, which is what it was designed to do. But, the mil-dots themselves are handy little aiming indicators and there are many ways you can use them that does not involve estimating range. A single millradian is a fixed unit of measure much like a MOA, and as such we can use our mils for holds and leads. Or as some people call it “Kentucky Windage”. This is where you hold above a target that is further away from you than your rifle is zeroed for. We know that a millradian is 3.44 MOA, and as such we can now create our own windage or elevation hold offs. Lets look at the .308 match load with a 175gr Sierra Match King at 2600fps. Below is a table for the windage hold offs in inches, and mils.
|Federal GMM 175gr 2600fps – 10mph Crosswind|
Now, the mil values I listed are rounded to the nearest tenth (.1) because that is about as accurate as one can estimate using the mil-dot reticule. It might be suggested (I do it) to break these values down to the nearest half mil (.5). The reason is because its much easier to remember, and easier to aim at half and whole marks on the reticule. Its going to get your close enough for a hit. Of course, if you are shooting bull’s-eyes in competition, then this method is not recommended. For fast, easier to remember values to hold off for wind, moving targets, and distance changes, make up your charts as we did above and using half mil increments for your specific ammo, and then memorize them for field use. The one major problem with this method is that if you are holding off for both windage and elevation, you will be aiming in “space”, which makes accurate aiming points extremely difficult. As one final example, below is a chart for a 500 yard zero, with mil hold values for 100-800, rounded to the nearest half mil. You can take the ballistics as far as you want, but this would be a realistic table for field work.
|Federal GMM 175gr 2600fps – 500y Zero|
Notice how easy this particular table would be to memorize. Zeroed at 500, just drop 1 mil for each 100 closer, (except at 100) and then rise by 1.5 Mil for each 100 over 500. Again, these will get you hits, but not bull’s-eyes.
This concludes my discussion about mil-dots. If you have any further questions or would like some more information added, please email firstname.lastname@example.org and we’ll see what we can do.