By Ian Kenney
Milliradian based reticles have been utilized in riflescopes since the 1970’s when the US Marine Corps adopted the Unertl 10X scope for their M40A1 sniper rifles. The scopes had a mildot reticle installed in the scope to aid in ranging a target at an unknown distance to increase the probability of a first round hit. Today, a mil-based reticle of some sort can be found in the riflescopes of military, law enforcement, and civilian shooters all around the world. A mil-based reticle is a multi-functional tool that includes the ability to estimate the range to a target, compensate for the trajectory of the bullet, and speed up the zeroing process.
First allow me explain what a milliradian is. A milliradian is a unit of measure typically used in engineering to derive angles from a circle, which is similar to another unit of angular measure common to most shooters, the minute of angle. The difference between the two however is that the milliradian is a coarser unit of measure than the minute of angle, meaning one milliradian will extend farther than one minute of angle. There has been some debate however as to the exact MOA values of some mil reticles going back to the first mildot reticles used by the US Army and USMC. For the purposes of this article, however, I will only use the engineering specification of the milliradian since most of the mil-based reticles in use, are based around it. These include reticles from Premier Reticles, Schmidt & Bender, Leupold, Nightforce, and so on.
The specifications of a milliradian are:
360° Circle = 6283 Milliradian
One Milliradian = 3.6” @ 100 yards
One Milliradian = 3.438 MOA
One MOA (True) = 1.047” @ 100 yards
Mil-based Reticles and Mil-based Adjustments
Most tactical riflescopes employ a mil-based reticle of some sort and below I’ve included a couple examples of mil-based reticles.
Mil-based reticles can be found in many of the tactical riflescopes on the market, however the exact dimensions of the mildots, or hash marks, can vary from manufacturer to manufacturer. For example the Premier Gen II reticle uses a mildot that is .2 mils in diameter while the US Army mildot found in the Leupold M3A uses a .22 mildot. This is why it is important to learn the subtension of the mil-based reticle you will be using to mitigate any possible mistakes. Knowing the correct subtension of the reticle will also aid the shooter in being able to precisely break the reticle down and accurately judge the distance to the target.
As useful as a standard mildot can be, reticles such as the Nightforce MLR and Premier Gen II offer features that enhance the mil-based reticle, making it easier to use and more versatile. Mil-based reticles like the MLR and Gen II offer half mil hash marks that make it easier to break up the reticle for easier ranging and more accurate trajectory compensation. In addition to half mil hash marks, some reticles offer hash marks at the end of the reticle that break the milliradian down to even finer increments to aid in even more accurate range estimation.
In addition to mil-based reticles, some manufacturers will also make the elevation and windage adjustments milliradian as well to match the adjustments to the reticle. The most common click value when talking about milliradian adjustments is one click being equal to 0.1mrad or one click being equal to .36” @ 100 yards or 1 cm @ 100 meters. Therefore ten clicks will equal one milliradian or 3.6” @100 yards or 10 cm @ 100 meters. Just like when using MOA, the value of the milliradian increases with distance. At 200 yards one milliradian will cover 7.2” and at 300 yards it will cover 10.8”, and so on. Matching the reticle and the elevation/windage adjustments has some distinct advantages over scopes that use a mil-based reticle with MOA adjustments. When the adjustments are matched, what the shooter sees in the riflescope as far as a necessary correction is simply what needs to be dialed into the scope. Scopes that have 1/4 MOA adjustments will require a conversion in order to get the proper elevation and/or windage adjustment.
Here is a table of conversions:
MOA to Milliradian
Milliradian to MOA
MOA Value ¸ 3.438 = Mil Value
Mil Value X 3.438 = MOA Value
7.25 MOA ¸ 3.438 = 2.1 Mil
2.1 X 3.438 = 7.25 MOA
Using the Reticle to Range an Unknown Distance Target
Ranging a target that is an unknown distance away from the shooter is something that mil-based reticles were designed to do from the start. However, using the reticle for this purpose requires a lot of practice to become truly proficient and get accurate range estimates for distant targets. In order to effectively use the reticle to range the target, the shooter must know the size of the target he is ranging, in order to complete the necessary math equation.
When doing range estimation with a mil-based reticle, use the following equations to get a distance to the target.
For distance in yards: (27.77 X Target Dimension) ÷ Mil Reading = Range
For distance in meters: (25.4 X Target Dimension) ÷ Mil Reading = Range
The first step in getting an accurate range estimate is to get into a steady position, typically a prone position, and align the reticle with the target. When aligning the reticle, place the crosshairs on the 6 o’clock edge of the target or at one of the bottom corners. The thick post of the crosshair can also be used instead of the crosshairs when getting a mil reading.
The next step is to measure the height and width of the target in mils and plug those figures into one of the math equations given above. In this case we’ll use the equation for yards.
(27.77 X 40”) = 1110.8 ÷ 2 mils = 555 yards
(27.77 X 20”) = 555.4 ÷ 1 mil = 555 yards
When doing range estimation using a mil-based reticle it is always best to range both the height and width of the target and average the two figures together to get the best estimate possible of the range to the target. In this case, both mil readings yielded the same distance so we can figure the target is just past 550 yards and the appropriate amount of dope needs to be put on the scope.
Here is another example of using the reticle to range a target.
The disc extends to just below the second mildot, since this is a Gen II reticle the dots are .2 mil in diameter, making the mil reading 1.9 mils. Since height was checked first, check the width next to confirm the mil reading. Plug the mil reading into the range estimation formula and you will get a range of 146 yards.
The above equations can be performed on a calculator, however the easiest way I’ve found to get the range to a target when using a mil-based reticle is to use a Mildot Master. The Mildot Master is a sliding scale calculator that can help make fast, accurate range calculations in yards or meters. Additionally the Mildot Master can make adjustments for slope to the target and it even has an area to affix ballistic information. Mildot Masters can be easily purchased from online retailers like US Tactical Supply and others who stock data books, slope dopers, and other precision rifle accessories. When you purchase the Mildot Master though, be sure to thoroughly read the instructions to fully understand the Mildot Master’s capabilities.
Another method of fast range estimation without a calculator is a mil relation chart like the one pictured below. A mil relation chart, or cheat sheet, is a spread sheet that has target sizes along the top and mil readings down the left side. To use this chart simply find the target size and the mil reading and then trace along until you find the yardage where they intersect. This method is not perfect since it only provides ranges for the targets and mil readings listed, anything in between would require some guess work, but it works in a pinch.
Considerations When Ranging
When performing range estimation with the reticle, some environmental factors can make getting accurate ranges difficult. For example, if it is hot and humid outside, mirage can severely obscure the edge of the target making it difficult to get an accurate mil reading since the edges of the target would appear wavy. Another factor that needs to be considered when performing range estimation is the targets relationship to the shooter. If the target if facing away or down from the shooter, the mil readings will be skewed by the angle and an incorrect range estimate will result. If the target is facing turned at an angle facing away from the shooter it is best to get a mil reading for only the height of the target. If the target is facing downwards or the shooter is looking down at the target, it is best to range the width of the target since it will be less skewed by the angle.
Practice, Practice, Practice
When it comes to ranging an unknown distance target practice is the only way to stay proficient at breaking the reticle down and performing the calculations in order to get an accurate range estimate. Range estimation using a mil-based reticle is a perishable skill and one that fewer and fewer people are learning given the proliferation of laser range finders. While laser rangefinders are excellent tools, they should not be the only means of obtaining a range since batteries die and electronic components can break. One way to practice range estimation is to range targets that are a known distance away and check your estimate to the actual distance. Another method is to range an unknown distance object and then check it using a laser range finder. However you practice range estimation though, always use safe firearms handling practices and ensure the weapon is unloaded before you get down behind it or use a spotting scope with a mil-based reticle.
Using a Mil-Based Reticle For Trajectory Compensation
A mil-based reticle can also be used to compensate for the trajectory of a round to make a fast follow up shot or to engage multiple targets at varying distances.
Follow Up Shots/Zeroing:
A mil-based reticle excels at allowing the shooter to make fast and accurate follow up shots should the first round miss and the splash was observed.
Here the shooter’s first shot was off target but the shooter observed the splash 2 mils right and 1 mil below the desired point of impact. All the shooter has to do is bring the reticle up 1 mil and left 2 mils and fire again, impacting dead on target. This method works well when a time limit or shifty winds make attempting to dial the correction into the scope impractical.
In the same way the reticle was used to rapidly engage the target with a follow up shot the same process can be used to zero the scope by “reading” the reticle. Using the above example, the shooter notices the impact 2 mils right and 1 mil low from his desired point of impact. To zero a scope that has milliradian adjustments, all that is needed to zero the scope is to dial 2 mils left and 1 mil up. Confirm the correction by shooting a group and the zeroing process is complete. With a scope that has MOA adjustments a conversion will have to be performed in order to figure out the proper amount of adjustment. This is why it is highly recommended that the scope have a matching reticle and adjustment configuration.
Multiple Targets, Multiple Distances:
The mil-based reticle is very effective at engaging multiple targets at varying distances when the scope is set to a mid-range zero and the reticle is used to compensate for targets farther out and closer in than the zero distance. This technique requires some practice but when a shooter achieves a good level of proficiency, it can be surprising how fast targets can be engaged.
This technique works best if the drop data is in milliradian. If it is in MOA use the conversion equation to convert it to Mrad.
The first step is to use a mid-range zero to set the scope too, I like to use a 400 yard zero since 100-600 yards is generally no more than 2.0-2.5 mils above and below the crosshairs.
Once a mid-range zero has been chosen, subtract that distance’s mrad value from the other zero values to determine the hold over or under points on the reticle.
2.6 mrad - .7 mrad = 1.9 mrad, which would be the hold under point for a 200 yards using a 400 yard zero.
Below are the data card and an example of a mil hold over diagram for M118LR.
I’ve found that this technique works best with the magnification is set to about 8X-10X depending on the distance to the target and how spread out they are. It also helps if the scope has a first focal plane reticle, since I can dial the scope to any magnification and the reticle will still be correct. Scopes that have second focal plane reticles are normally only correct at the highest magnification and going to a lower power can make calculating the hold points more challenging.
The reticle can also be used to compensate for the effects of wind on the bullet’s trajectory instead of attempting to dial the correction in. This works well in shifty winds or under other time constraints when dialing the wind correction into the scope is impractical. Again, this technique works better if the drop data is in milliradian since the correction is easily applied to the reticle.
The target is 400 yards away with roughly a 10 mph wind coming from the left.
Look at the data card and see what amount of hold is necessary.
Hold left of the target, since the wind will push the bullet right, and place the 1.0-mil mark on the center mass of the target.
Using the proper fundamentals of marksmanship the bullet should impact in the center mass of the target.
This technique is very effective to the point that many long-range shooters rarely use the windage knob to correct for wind since this technique is just as accurate and can react to shifting winds faster.
Of course, the only way for this technique to be truly effective is to get out and practice reading the wind and then applying that to actual long-range shots. Sometimes it’s helpful to use a personal weather station to help confirm wind estimates or see how different wind speeds effect the environment. For instance what a 15 mph wind does to tree branches and grass is quite different from what an 8 mph wind would do to the same objects. Just like when using the reticle to range with the only way to become really good is to practice, practice, practice.
In much the same way the reticle was used to compensate for wind, the reticle can also be used to engage moving targets. The amount of lead necessary will depend on the distance of the target, the speed of the target, and the time of flight of the bullet.
There are a couple of formulas though that will help calculate the hold required to engage a moving target.
To figure the lead from center mass in feet multiply the time of flight in seconds by the target speed in feet per second
.7 second TOF X 4 fps = 2.8 feet lead from center mass
To figure out the lead in milliradian use the following formula:
(Lead in feet X 12) – 6 ÷ (Range X .035) = Mil Lead from Leading Edge
(2.8 ft x 12) – 6 = 27.6; (500 yds X .035) = 17.5; 27.6÷ 17.5 = 1.6 Mil Lead
Keep in the mind that even though the mathematic formulas give you a lead to use, it doesn’t necessarily mean that it will be perfect. In reality leading a target requires practice and data collection since a person may lead a target differently for a target moving 4 fps from right to left than they would leading a target going from left to right.
In the End
Mil-based reticle are an incredible tool for the long range shooter that can perform a variety of functions that can help get rounds from the point of aim to the point of impact. However, as I stated many times above, using mil-based reticles effectively requires a lot practice to gain and maintain proficiency in estimating range and compensating for the trajectory of the round. Whenever practicing though I want to stress to always use safe firearms handling practices and ensure the rifle is UNLOADED before you get down behind the rifle.