-- by Kent W. Gooch, CWO2, USMC (ret)
Over the last couple of years the mil dot reticle has become less of an option and more the standard in tactical rifle scopes. Since its inception with the Unertl USMC sniper scope and later in various versions of the Leupold Mark IV scope, military snipers have come to know the mil dot reticle as a reliable means of determining distances to targets, establishing leads for moving targets, and for alternate aiming points for windage and elevation holds. Military snipers who are graduates of formal programs of instruction have spent numerous hours honing their ability to use the mil dot reticle and are comfortable and competent with it. Military snipers are easy to train on the mil dot reticle, as the military has been using the mil relation formula in one form or another for many years. As the WERM rule (width of correction = Range x mils observed), it has been the mainstay for determining adjustments when calling and adjusting indirect fire weapons such as mortars and artillery. On the other hand, some Law Enforcement and civilian tactical and practical long-range precision shooters are a little hesitant sometimes of the mil dot reticle because of a lack of proper training. I hope this article will help remedy this problem.
The mil dot reticle is a post and wire reticle with 10 mils (milliradians) between opposing posts and dots spaced 1 mil apart on the wires, minus the reticle intersection so
as not to obscure the aiming point. A milliradian is an angular unit of measure that just happens to equal one yard at 1000 yards and 1 meter at 1000 meters. Knowing this fact we can, through the wonders of elementary mathematics, use this little critter to determine distance to an object when the size of the object is known. The sniper simply measures his target using the dots, then works a simple formula to obtain the targets distance or the distance to an item near the target.
How the milliradian became the unit of measure of choice is fairly interesting as sniper trivia. Back when the military was determining how to graduate their artillery pieces the techno-geeks settled on the milliradian as the unit of measure for their sights. Since there were 6,283 milliradians (2 PI for all you math whizzes) in 360 degrees they rounded up to 6400. The Soviets on the other hand rounded down and ended up with 6200 mils in a circle for their artillery sights, compasses, etc.
As the Marine Corps sniper program grew and matured during the late 70s, the snipers desired more accurate range estimation abilities than what the issue 6x30 and 7x50 binoculars and the 3x9 Redfield scope were allowing. The binoculars had hatch marks that were graduated in 10 mil increments with the actual hatch mark lines being 5 mils long (Steiner M22), which were all too coarse for obtaining much precision. Add to this that the Accu-trac system in the Redfield, using an 18-inch stadia line intended for deer hunting, left much to be desired for tactical shooting. We at the Scout/Sniper Instructor School used a "barber pole" to teach students to mentally break the reticles of the binoculars into finer subtensions than for what the binoculars were originally designed. This barber pole had 4" bands painted on it and we set it out at 111 yards where each band equaled 1 mil. This allowed the student to see what the graphics on the reticle subtended including hatch marks, numbers etc. For example, the base of the number 2 equaled a certain fraction of a mil and the tips of the number 3 equaled another number of mils. All of this was fine and dandy but a better way was needed.
Although the mil dot system is both simple and accurate, as with anything else it does have limitations, especially if you havent received formal training on them. The owners manuals that usually come with the civilian scopes are very basic when they explain the use of the reticle. I've been teaching the use of the things for over 18
years and have seen most of the problems that students run into when first encountering mil dot reticles. Even high-tech devices such as laser range finders have limitations and disadvantages and low-tech mil dots are no exception. In this article I will cover some facets of mildot usage that will enhance your ability to use them.
The Mil relation formula. There are a couple of permutations of the mil relation formula floating around. At first look most of them strike fear in the hearts of most of us Neanderthal, knuckle dragger types, but they are really quite user friendly. Granted the formulas require you to use more than your fingers and toes, but we Marines can handle it! Well, here we go. The basic one is:
Height of item in yards (meters) x 1000/Mils read = Distance to item in yards (meters)
This formula is good when the sniper knows an items size in yards. My only problem with this version is that cops often have to deal with small items such as vehicle wheels, small stickers on windows, headlights etc. This requires the officer to convert a 7" headlight into a decimal equivalent in yards before they can work the formula. And since most cops are fellow Neanderthals and are usually under a fair amount of stress to begin with, I prefer to teach the formula:
Height of item in inches x 27.8 (25.4)/Mils read = Distance to target in yards (meters).
The formula can be worked backwards in training so that if the distance to the target is known we will know what the mil reading should be. This is handy for beginners learning to read mil dots. The formula for this is:
Size of item in inches x 27.8 (25.4)/Distance in yards (meters) = Mils
Knowing the sizes of items being measured is a matter of knowing your prospective area of operation and making a list of the sizes of standard items. Make sure you get both height and width of objects as you can mil both dimensions but the largest dimension mathematically will usually give the most accurate answer. Military snipers should have sizes of enemy vehicles, enemy weapons, average heights of soldiers, etc. An LE sniper should have sizes of traffic signs, bricks, license plates, etc. So carry a tape measure and a notebook with you and prepare to have people look at you funny as you measure curbs, traffic lights, mailboxes and other commonly found objects in your area of operation.
So as you can see the mil relation formula shouldnt scare anyone off. As a matter of fact there are ways to make the use of the formula even easier. Many databooks such as the TRGT data book and others have charts developed using computer spreadsheets that allow the shooter to find the target size and the mil reading on the chart and it gives the shooter the distance without any hate or discontent. You can even make your own using the above formulas if you know how to use a spreadsheet such as MS Excel.
The EASIEST way to deal with this formula is to get yourself a MILDOT MASTER. This handy slide-rule type device does the calculations for the mil relation formula, corrects for target size when viewed at angles, corrects for slope, gives MOA/mil/in equivalence and even predicts the future. (You have to bury some chicken bones and some other stuff to get the last feature).
Reticle Focus. The first thing we will talk about is reticle focus. In order for the sniper to obtain precise mil readings the reticle must be properly focused. If the reticle is out of focus, the reticle will appear fuzzy and go in and out of focus as the eye attempts to zero in on it. Not only will mil readings be difficult to obtain but the sniper will also suffer eye fatigue over long periods behind the scope as the muscles of the eye attempt to maintain focus. Steps for focusing a scopes reticle are:
- Look at a distant object (about 300 yards) and allow your eyes to become focused on it.
- Quickly look through the scope at the sky or a blank wall and check to see if the reticle is immediately sharp and crisp. If it is, then no further adjustment is needed.
- If your eye has to re-focus AT ALL on the reticle then proceed.
- Grasp the eyepiece and back it away from the lock-ring. Turn the eyepiece several turns so as to move at least 1/8". It will take this much change to achieve any measurable effect on the focus. Then repeat step one.
- If the image is better, continue to turn the eyepiece in the same direction. If it is worse, turn the eyepiece the other way and repeat the previous steps until the image of the reticle is sharp and crisp immediately upon looking into the scope.
- Do this several times. Taking the focus past the point of best focus and back again will help to ensure you have the clearest setting. Then lock up the eyepiece by screwing the lock-ring back to the eyepiece.
- Some scopes feature a quick-adjust eyepiece and therefore simplify this operation.
Target/Objective Focus. One area that is often overlooked when ranging with mil dots is target focus. If the target is out of focus it will either read slightly larger or smaller than it should when properly focused.
There have been many occasions while working as an instructor where I have found students do worse on ranging with mil dots than with binoculars or even the naked eye. Most of the time this ceases to be a problem after they begin ensuring that both the objective and the reticle are sharply focused.
Ambient Light Conditions. As with all other methods of range estimation that uses the snipers eyes, the nature of the ambient light conditions can affect the snipers ability to obtain an accurate mil reading. Effects such as glare, mirage, haze/fog can obscure the target or alter how the sniper sees the edges of the target which will all cause inaccurate readings. In order to deal with this, a sniper must practice obtaining mil readings in all weather conditions and take notes as to corrections that he must make in those conditions. For example a sniper knows that in foggy conditions he needs to add .1 mil to his mil readings or in bright sunny conditions he has to subtract .1 mil on light colored targets due to glare. So practice obtaining distances with your scope in all conditions and confirm distances with a laser range finder. Keep notes as to how different light conditions alter your mil readings.
Hang on a minute!! Use a laser range finder to confirm distances? You are probably asking, "Then why the hell worry about mil dots if I have a laser range finder?" Well, have you ever had batteries die on you or have a piece of electronics go belly up? Also, have you heard of laser detectors? Besides, mildot reticles have other uses besides ranging. Okay, now that we've cleared that up Ill continue.
Okay, lets look at what we have up to this point. We've learned that we have to make sure our reticle and target are in focus. No problem here as we should have these items under control anyway. We've had to either learn a simple formula or buy a MILDOT MASTER. No big deal here either. All we are left with now is to figure out how to measure objects with the reticle. Lets see if there are any major obstacles here.
Reading the Dots. The precision tactical shooter must be able to obtain accurate mil readings to the tenth of a mil. This is where it is important to know the subtensions on your reticle. For example, I know in my Leupold 3.5 x 10 M3LR with the USMC stamped wire reticle pattern, the dots themselves are .25 mils and the posts are 1 mil wide when the scope is at maximum magnification (more on this in a minute). In Leupold scopes with round, dot-etched glass reticles the dots are .22 mils in diameter and the posts are .5 mils wide. This enables me to break the reticle down as in the illustrations above right.
The importance of being precise on your readings becomes evident when working at long range. For example, if a 40-inch target (the size of a kneeling man) is incorrectly measured at 1.5 mils it would range out to 740 yards where if the correct reading were 1.6 mils it would actually be at 693 yards.
Assuming there is 5 MOA drop with a .308 between 700 and 800 yards you could be dialing on around 2 MOA too much elevation. At 700 yards that is 14 inches and may put you over the target depending on your aiming area. So here are some helpful tips when measuring a target.
- Have a steady rest for your rifle. Just as steady as when you are firing. Lay the rifle on its side if you have to.
- Use a post for one end of the measuring scale if possible. This will give you a clear point for one end of your measurement.
- Make sure the target/reticle are focused.
- Practice obtaining mil readings on targets at known distance. Using the formula given above determine how many mils a target should read then work on it until you can see that measurement in the scope.
Variable Power Scopes. My last tip there brings up an interesting point in regards to variable power scopes with mil dot reticles. Most American variable power scopes do not magnify the reticle along with the target. In other words the reticle remains the same size as the target image zooms. This can wreak havoc if you try to measure a target at the wrong magnification, as the dots will only equal 1 milliradian at one magnification setting. Knowing what magnification setting your scope is set up to use the dots on is CRITICAL to getting accurate readings. Most scopes are set up to use their highest power setting and some have an index mark on the power ring. One problem I've noted with the variable power scopes is that the setting that the factory tells you to use can often be off a bit. I've had students be constantly off on readings by 1 or 2 tenths and get flustered as hell. Some of this can be due to out of focus reticles but many of them figure out that the index mark is off a hair. By using the barber pole I mentioned earlier, you can find the EXACT point where the mil dots subtend precisely 1 mil. As a side note you can also find the point where the dots equal 2 mils and other readings.
Other uses of the Mil Dot Reticle. I think we've pretty much exhausted material on the mil dot reticle as a ranging tool. I will now go into its other uses in establishing alternate aiming points for moving targets, elevation/windage hold-offs and quick follow-up shots. As with any tool in our toolbox, the more we know about it the better off we are. If I can use a piece of gear for more than one purpose it becomes more valuable than a highly specialized piece of gear such as a laser range finder. (Although lasers make nice paperweights and Frisbees when their batteries die or the light conditions render them useless.) These other uses are just as valuable as the primary range finding purpose of the mil dot reticle.
Leads for Moving Targets. When a shooter is training on moving targets he should be taught to calculate leads for moving targets knowing the targets speed, time of flight of the bullet and the targets direction of movement. The formula is:
Time of flight (sec) x Speed of target (fps) = Lead from center-mass in feet (full value lead)
Since it is easiest to establish a lead from a targets leading edge and we want a lead in mils we will then use the formula:
(Lead in feet x 12) - 6
(Range x .01) x 3.4
We can now use our mil dot reticle to hold off instead of having to guess at target widths and other not-so accurate methods. This formula is a bit ungainly to use in tactical situations, and it doesnt take into account different shooters reaction times, but it should be used in training to determine starting leads when engaging live fire moving targets. The shooter then fine tunes his leads and writes them in his databook.
Elevation/Windage Hold-Offs. Mil dot reticles can also be used for alternate aiming points for elevation and windage holds, as there are often situations where a sniper may not have time to dial on his elevation and sight settings. Snipers often have to deal with targets that appear unexpectedly, multiple targets at different distances, gusting winds of varying direction and the thing we all dont want to think about, a miss or an insufficient hit. In these situations the shooter often doesnt have time to deal with turret caps, 1/4 MOA target turrets, or in the case of the miss or insufficient hit, changing the sights. In these occasions, WHEN EXTREME PRECISION IS NOT A REQUIREMENT, it is better to establish an alternate aiming point with the mil dot reticle and hit the target.
Windage Hold-Offs. When the USMC Unertl scope first came out in 1981-82, it only had 4 MOA of windage in each direction. As anyone who has shot past 300 yards knows, that isnt enough windage to handle windrift caused by your buddys heavy breathing from the next firing point. So we had to use the mil dots for windage. This is a simple feat if you just remember that 1 mil is 3.5 MOA. So if I need 3.5 minutes of right windage I leave "0" windage on the windage knob and hold 1 mil dot right of center mass. If I need 4 MOA then I hold a tad more than 1 mil dot. 2 mils? Hey, remember when we broke the mil dot reticle down for precise measurements when determining distances? Its the same deal with wind hold-offs. Break the mils into thirds and you have 1 MOA hold points; okay, so its 1.13 MOA hold-offs, big deal.
Elevation Hold-Offs. Now lets talk about elevation hold-offs. In order for us to use a mil dot reticle for elevation holds we have to determine from what sight setting we will be holding off from. In most situations this will mean that we will leave a certain sight setting on the rifle when not set for a specific target. This is very similar to the military battle-sight zero concept where an M16A2 is zeroed for 300 meters, which allows the rifleman to engage targets from 0-325 meters by just aiming center mass. In US Army doctrine with the M24 sniper weapon system and M118LR ammunition (175 gr. Sierra BTHP @ 2600 fps) the sniper leaves his 500m zero on the scope with zero windage. Then by using the elevation holds in the chart below, he can get rounds on target without taking the time to change his elevation setting. Another use for mil dots is when we have to engage multiple targets at different distances and we have time to set it up. We know that if we have to engage a target at 600 yards then drop down to 300 yards and drop another one all we have to do is calculate the elevation difference between 300 and 600 yards then dial on the elevation for 600 and hold low for the 300 yard shot. In this case I know that there is 7.5 MOA difference between the 600 and 300 yard shot. So after engaging the 600 yard target with my 600 yard sight setting, since it is the more difficult shot, I will then hold 2 mils under the 300 yard target and engage it. The .5 MOA error (1.5 inches at 300 yards) in hold is nothing to worry about in MOST situations.
Follow-up Shots. The last thing I will talk about in regards to the mil dot reticle is its usefulness when firing rapid follow-up shots when a quick correction in elevation or windage is required. In these situations a follow-up shot is needed quickly! If the first shot was a miss, it wont take the target long to figure out what is going on. If he is trained or just real smart, as soon as he hears the crack of the round or some result of its impact he is gonna move. But in many situations the target wont move due to ambient noise masking the shot or just plain stupidity as in the case of the FBI field SWAT snipers that got off 3 shots at a hostage taker without the perp figuring out what was going on. (In this case the snipers shots were hitting a low wall in front of the rifle that the sniper didnt know was in the way. The third shot hit home after the sniper raised his position.)
In the case of a well fired shot that missed or was off-center, the observer can give the sniper an alternate aiming point using the mil dots as with windage holds. If the shot was at 200 yards and it was 4 inches (2 MOA) low, the observer tells the sniper to hold 2/3 mil high and fire again. This is all assuming of course that the sniper calls the first shot a good shot. If he called the shot low, then the sniper should fire center again and pay attention to the fundamentals this time.
And you thought that all mil dots were for was range estimation, didnt you?
I hope this information has shown you that mil dots are a valuable aid for the precision tactical shooter/sniper. It may seem like a lot of information at first but as you absorb this stuff remember that much of it can be simplified with aids like cheat sheets, crib notes and through the use of devices like the MILDOT MASTER even us Neanderthals can handle mil dots. Those that cant or refuse to use them are missing out on a valuable tool. But thats okay. Those batteries in that laser are probably okay.