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What is a Mil Dot reticle ? |
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Chris Farris
TEAM SWFA - Admin swfa.com Joined: October/01/2003 Location: Texas Status: Offline Points: 8024 |
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Posted: May/10/2004 at 16:49 |
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The Mil Dot Reticle
Simply put, the Mil-Dot is a range estimating reticle that was developed for military applications. The space between the dot centers subtends one milliradian (Mil). One Mil subtends 3.6" at 100 yards, or 36" at 1,000 yards.
This reticle was developed in the late 1970s to help U.S. Marine snipers estimate distances, and is now standard for all military branches. The space between dot centers subtends one milliradian (mil) hence the name mil-dot. Contrary to popular belief it does not stand for "military dot". One mil subtends 3.6 inches at 100 yards or 36 inches at 1,000 yards. To use this system effectively you must know the size of the target. For instance most people are an average of 6 feet tall or 2 yards. The formula used for determining range to the target is (size of target x 1000 divided by number of mils the target covers).
You can do these calculations with a calculator or use a reference table like the ones listed below. But remember that your answer is only as accurate as the numbers you plug into the formula. An error of just a 1/4 mil will cause an error in target range. Also an error in estimating the size of your target will cause an error in target range.
The top line on the table represents the size of the target as measured in feet or inches. The second line represents the conversion of the foot measurements to yards. The left column shows the mil measurements to the nearest 1/2 mil. The mil scale can be split to the nearest 1/8 mil for a more accurate range measurement. To use the table follow the instructions below.
Range Estimating with the Mil-Dot ReticleDots are spaced in one mil (milliradian) increments on the crosshair. Using the mil formula, a table can be created like the ones above that is based on the size of the object being targeted. Just look through the scope, bracket the object between dots, and refer to the table for an estimated distance to target. The radian is a unit-less measure which is equivalent in use to degrees. It tells you how far around a circle you have gone. 2 PI radians = 360 degrees. Using 3.14 as the value of PI, 6.28 radians take you all the way around a circle. Using a Cartesian coordinate system, you can use "x"- and "y"-values to define any point on the plane. Radians are used in a coordinate system called "polar coordinates." A point on the plane is defined, in the polar coordinate system, using the radian and the radius. The radian defines the amount of rotation and the radius gives the distance from the origin (in a negative or positive direction). The radian is another measurement of rotation (the degree/minute/second-system being the first). This is the system used in the mil-dot reticle. We use the same equation that we used before, but, instead of your calculator being in "degree" mode, switch it to "radian" mode. One milliradian = 1/1000 (.001) radians. So, type .001 into your calculator and hit the "tangent" button. Then multiply this by "distance to the target." Finally, multiply this by 36 to get inches subtended at the given distance. With the calculator in "radian" mode, type: tangent(.001)*100*36 = 3.6000012 So one milliradian is just over 3.6 inches at 100 yards. If we extrapolate, two milliradian equal about 6 feet at one-thousand yards. The mil-dot reticle was designed around the measurement unit of the milliradian. The dots themselves were designed with this in mind and the spacing of the dots was also based upon the milliradian. This allows the shooter to calculate the distance to an object of known height or width. Height of the target in yards divided by the height of the target in milliradians multiplied by 1000 equals the distance to the target in yards. For example, take a 6-foot-tall man (2 yards). Let's say that the top of his head lines up with one dot and his feet line up four dots down. So: (2/4)*1000 = 500 yards away. This same technique can be used to estimate lead on a moving target or to compensate for deflection on a windy day. The distance from the center of one dot to the center of the next dot is 1 milliradian. We are told (by Leupold) that the length of a dot on one of their reticles is 1/4 milliradian (Given this much information, one can determine that the distance between dots is 3/4 milliradian.).* I use the term "length" because the mil-dot is not round in all cases. It is oblong in some scopes and round in others (Tasco). The width of each dot is an arbitrary distance and is not used for any practical purpose. Like a duplex reticle, the mil-dot reticle is thicker toward the edges and uses thin lines in the middle where the dots are located and the crosshairs cross. The distance between the opposite thick portions is 10 milliradian on Leupold scopes. *NOTE: 1/4 milliradian = .9" and 3/4 MOA = .785", so, obviously, a mil-dot cannot be both 1/4 milliradian and 3/4 MOA. The maker of the mil-dot reticles for Leupold explains: the dots on their mil-dot reticles are 1/4 mil. They are not 3/4 MOA. Apparently, Leupold just figured that more shooters understand MOA than milliradian, so they just gave a figure (in MOA) that was close, but not super precise. To use a mil-dot reticle effectively, all one need remember is that the distance between dot centers is 36" at 1000 yards. This lets you determine the range of a target of known size. At that point, you can dial the scope in for proper elevation OR use the dots to hold over the proper amount. The dots on the horizontal crosshair can be used to lead a target (if you know the range to the target, then you'll know the distance between dots, and thus the distance to lead) or to compensate for deflection. If you own a mil-dot scope or are going to in the future you need to check out this new product called The Mil Dot Master. Minute-Of-AngleThe term "minute-of-angle" (MOA) is used regularly by target shooters at the range, but is probably understood thoroughly by few (the same goes for mil-dots). Defined loosely, one MOA = 1" @ 100 yards; so, if you shot your rifle 5 times into a 100-yard target and every shot went into a one-inch circle you had drawn on the paper, then your rifle could be said to shoot 1 MOA. Likewise, if every shot goes into a two-inch circle at 200 yards, then you're shooting 1 MOA. A 10-inch group at 500 yards would be 2 MOA. Now for the fun part. There are 360 degrees in a circle. Each degree can be broken down further into minutes. There are 60 minutes in a degree. Likewise, there are 60 seconds in a minute. Now, to figure out the dist |
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Chris Farris
TEAM SWFA - Admin swfa.com Joined: October/01/2003 Location: Texas Status: Offline Points: 8024 |
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OK, so now you understand what it is and now you want to know.......How to Get the Most out of your Mil Dot ReticleOver 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 target's 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 milliradian (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 70's, 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 sub-tensions 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 haven't received formal training on them. The owner's 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 item's 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 backward 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 shouldn't scare anyone off. As a matter of fact there are ways to make the use of the formula even easier. Many data books 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 The Mil Dot Master. This handy slide-rule type device does the calculations for the mil relation formula, corrects for target size when viewed |
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Chris Farris
TEAM SWFA - Admin swfa.com Joined: October/01/2003 Location: Texas Status: Offline Points: 8024 |
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If your head doesn't hurt by now then here is even more info., but this one is in a PDF file so you can print it and read anywhere.
A sniper's perspective on the mil-dot reticle by Michael Haugen
(635kB PDF) depending on your connection speed it may take a while to download after clicking the link above. |
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Chris Farris
TEAM SWFA - Admin swfa.com Joined: October/01/2003 Location: Texas Status: Offline Points: 8024 |
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a note from the Leupold engineers:
What is a Mil (Mil Dot Reticle)
Mil Dots as aiming points
Why is Leupold Mil Dot reticle a round dot reticle?
Mil Dot Reticle
Range Estimating With The Mil. Dot Reticle |
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jbyrd
Optics Apprentice Joined: April/09/2004 Location: United States Status: Offline Points: 21 |
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Thanks for the info.
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jeramiah
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Dammit man
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blaster
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Brady
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By now you are prolly burnt out on mil dots, but here is another helpful link.
Illustraded Mil Dot information Edited by Brady |
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Chris Farris
TEAM SWFA - Admin swfa.com Joined: October/01/2003 Location: Texas Status: Offline Points: 8024 |
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Roy Finn
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A 30 cabibre hone in a 1000 yard target. Sniper2
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sscoyote
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If u break down the mil-ranging formula and take a good look at it, it should become evident that the formula is not really mil-dot specific at all, and can actually be used with any reticle system with at least 2 stadia, as long as the stadia subtensions "fit" the target size well. The mil-ranging formula is simply a geometric formula that defines a certain stadia subtension at a certain range relative to another "subtension" or measurement at a different unknown range. This concept can be easily visualized if the user thinks of it as the spokes of a huge wheel that originate at the center, and go out to infinity at various angles, which can be 3.4 MOA , 5.0 MOA or 1000 MOA. It doesn't necessarily need to be the mil-dots 3.4 MOA. The next time u look through a scope with a plex, ballistic (like TDS), ranging, or custom reticle, try to visualize this concept (like a mil-dot, but just different subtensions). Let's just pick one as an example, say the Burris Ballistic Plex .308 hangun scope reticle. My 6.5-284 XP-100 Handgun has the 3-12X LER scope with Ball. Plex reticle. The subtension of the x-hair to upper post tip of the plex portion of the reticle subtends 3.1" @ 100 yds. Recently at a turkey shoot we were shooting a bowling pin at 600 yds. Before we shot i asked the Range Master if i could meaure the pin. It was 15" top to bottom. When we arrived at the station i pulled my calculator out and checked the system, by adapting the mil-ranging formula for the 3.1" subtension as follows:
tgt. size in inches x 100 yds./3.1"/portion of reticle tgt. brackets in tenths of the total measuring stadia.
The pin bracketed right @ .8 of the measuring stadia, so replacing the variables in the modified mil-ranging formula above derived the following:
15" x 100yds./3.1"/.8 = 605 yds.
The keen eye will note that the system is so flexible it can be used with any stadia-stadia subtension at any range-- even archery sight pins.
It should also be noted that any of the variables in the above equation can be an unknown such that stadia subtension could be calculated once tgt. size, range, and area tgt. occupies in reticle is known (helpful when attempting to calculate reticle subtensions of the Zeiss ZRF reticle or TDS, or even custom reticles when applied for rangefinding), or even tgt. size could be calculated once the other variables are known.
A more thorough breakdown of the system can be seen here under Reticle Rangefinding including ranging with more than 2 stadia ( Plex, Ballistic Plex, Varmint Hunter, custom reticles, etc.)--
www.ottllc.com/specialtypistols/sp20.pdf
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Steve
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Urimaginaryfrnd
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As you can see --- It's the Point of No Return !!!!!
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Chris Farris
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