Inside the Cross-Hairs
Inside the Cross-Hairs
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Joined: 2nd May 2014
23rd Mar 2015
Focusing your reticle
A reticle is the crosshair or aiming point in your field of view in a riflescope. To use a rifle scope reticle properly you must first focus it for your eye. Point your properly mounted rifle scope at the sky or a blank wall with the scope at its highest power. The eyepiece is adjustable on almost all rifle scopes. Some have a locking ring to prevent inadvertent movement. Loosen the locking ring and turn the whole eyepiece in or out a couple of full turns at a time until the scope crosshair is clear and sharp for your eye. Tighten the lock ring. On a fast focus (FF) eyepiece simply turn the ring until the reticle is sharp. On a fast focus eyepiece this may be only a fraction of a turn. Loosen the locking ring first, and tighten afterwards if applicable. Not all fast focus (FF) eyepieces have locking rings.
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The most basic reticles simply offer an aiming point. Fine crosshairs, Duplex, Nikoplex, 30-30, Heavy Duplex, or whatever the manufacturer wants to call them. They all give you a central aiming point. Thicker reticles show up better in low light or against busy backgrounds like foliage, and help draw your eye towards the center of your field of view. These reticle types are mostly used in hunting rifle scopes where extra precision is not a priority. Fine crosshairs, on the other hand can almost be invisible on a busy background, but excel at allowing you to adjust your shot in minute increments due to the small amount of target your crosshair covers up.
The amount of target your crosshair covers is called subtention. Fine cross hairs have minimum subtention. These are for accurate target guns mostly and easily disappear except on a clean paper target.
There are riflescopes with the reticle located in the first plane or the second plane. Almost all scopes for the American market have the reticle in the second plane. This means that the reticle does not appear larger as the magnification increases, just your target. Again, almost all scopes for the American market are in the second plane. First plane scopes increase the size of the cross hair with the target. Subtention stays the same. On second plane scopes, since the reticle size stays the same as the magnification increases, the subtention decreases. Less of your target is covered by your reticle. First focal plane scopes are offered by manufacturers like Schmidt & Bender, and a few by Leopold, Swarovski, and Barska and others.
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Bullet drop compensating (BDC) reticles
To understand how these reticles work you must first understand a bit about bullet trajectory. A bullet fired horizontally from a gun will hit the ground at the same time a ball will hit the ground dropped from my hand. Gravity accelerates objects at a constant 32 FPS. What will hit the ground first, a pound of bricks or a pound of feathers? Same. A bullet will hit the ground the same time as this ball, just a couple miles away. If I throw this ball to a person in the parking lot and aim at their chest the ball may land at their feet or bounce before them. I have to aim high to have the ball land at their chest. Same with a bullet. If a target is 100 yards away and my gun barrel is horizontal, the bullet will land low, just like the ball. And just like the ball, I have to aim higher to compensate for gravity’s effect on my projectile. How high depends on how fast I throw the ball and how far away my target is. Same with a bullet.
The most popular reticles being offered today by almost all manufacturers have some kind of BDC (bullet drop compensation) reticle in them. On second plane scopes the magnification has to be set at a certain power for these to work and you need known distances for these to be used correctly. A laser range finder is generally required.
Some very popular rifle scopes with compensating reticles today are the Swarovski BR, the Nikon BDC, the Zeiss Rapid Z, and the Leopold Boone and Crockett and Leopold Varmint Hunter’s. Again, most manufacturers will have at least one type of compensating reticle. Keep in mind that second plane American scopes will only work at a certain magnification designated by the manufacturer. Riflescopes in the first plane that increase the size of the reticle along with the target may be used at any power. Some way of range estimation is required for any compensating reticle. Again, use laser range finders. The lines in the reticle excluding the cross hair are called Stadia lines, and are used as aiming points for holdover. Beware, these are not exact. There are too many variables in gun barrels, ammunition, temperature, elevation, humidity, etc. When sighted in for a hunt at 300 yards here, I was about 10 inches off in elevation at around 7000 feet where the air was much thinner and the temperature cooler. You have to actually shoot the gun at specific distances rather than rely on a chart of any kind.
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Some reticles such as a mildot reticle can be used to calculate distance. Mil means milradian, not military. A milradian is 1/1000 of a radian. A radian is the angular measurement that is equal to the angle formed at the center of a circle by two radii cutting off an arc whose length is equal to the radius. A mil in a reticle subtends 3.6” at 100 yards. Double that number for 200 yards, triple for 300 yards and so on. A mil is 36” at 1000 yards.
To find the approximate distance to a target using mildot scopes you must first set the magnification at the required power specified by the manufacturer. Then you must know the approximate height of your target. A man may be 6’ tall or a torso may be 3’ tall. A full mil is from the center of one dot to the center of the next. If your target is covered by 2.5 dots, the size of your target is 2.5 mils. Now here’s the tricky part. Multiply the height of the target in yards x 1000 and divide by the height of your target in mils. (2 x 1000=2000 divided by 2.5 mils = 800 yards.) This is the approximate range to your target. You can see that it takes a while to calculate and that it is not the most precise way to measure for distance. It will certainly not tell you how high to aim or adjust, either, but the dots can be used for hold over if you know your trajectory. A mildot reticle is also pretty busy looking, and if you hold over, much of your target may be covered by dots. Military snipers normally deploy teams of two, with one shooter, and one doing the spotting and calculations. Mildots are rarely used anymore, with laser rangefinders being quicker and more accurate. Mildots will never be understood or used as designed by 99% of shooters but it makes them feel like Tactical Timmys. Bottom line; use a laser rangefinder to determine distance.
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Many scopes are offered with lighted reticles. This is so your cross hairs are visible in low light. The problem with this feature on inexpensive rifle-scopes is that even with adjustable lighting controls, the minimum brightness of the reticle is still too bright and immediately destroys any low light capabilities your eyes have developed, and often the reticles are so bright that you cannot even see your target. Top quality scopes have solved this problem through trial and error and minutely adjustable digital controls. Bushnell offers a Firefly reticle which glows after being charged with a flashlight, but is not adjustable.
The MilDot 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).
Height of target (yards) X 1,000 = Range (yards)/
Height of target (mils)
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.
Estimate height of target and locate across the top.
Measure height of target in mils and locate down the side.
Move down from the top and right from the side to find the range in yards.
Range Estimating with the Mil-Dot Reticle
Dots are spaced in one mil (milliradian) increments on the crosshair. Using the mil formula, a table can be created like the ones above that are 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 Leopold) 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 Leopold 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 Leopold explains: the dots on their mil-dot reticles are 1/4 mil. They are not 3/4 MOA. Apparently, Leopold 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.
The 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 distance subtended by 1 minute at any particular distance, we need merely to plug those two
values into a simple trigonometric equation. The tangent function fits the bill nicely. Here's the equation:
Tan (angle) = distance subtended/distance to the target
(Units must be consistent--e.g., 1/36 of a yard divided by 100 yards)
Now, we know the angle (1 minute or 1/60 of a degree) and we know the distance to the target (100 yards), but we need to figure out the actual distance subtended at the target (i.e., is 1 MOA actually 1" @ 100 yards?). What we need to do is solve for "distance subtended." Here's our final equation:
Tan (angle)*distance to the target = distance subtended
Make sure your calculator is in "degree" mode (as opposed to "radian" or "gradian"
and type in 1/60 (for degrees) and hit the "tangent" button. Then multiply that by 100 yards. This should give you the distance (in yards) subtended at 100 yards. Multiply this by 36 to get inches. The answer should be: 2X3.14X1=6.283/360=0.017452778/60=0.00029088X100=0.029087963X36=1.047197580733"
This is just a hair over the commonly quoted "one inch." At 1000 yards, this would be almost 10 1/2 inches. Apparently, it is just a coincidence that 1 MOA happens to be REALLY close to 1" @ 100 yards. It is, however, quite convenient.
The above reference of MIL-DOT and MOA are not linear they are angular so the key is reading the reticle like a you would read a tape measure or ruler.
Engagement of Moving Targets
Engaging moving targets not only requires the Sniper to determine the target distance and wind effects on the round, but he must also consider the lateral and speed angle of the target, the round's time of flight, and the placement of a proper lead to compensate for both. These added variables increase the chance of a miss. Therefore, the Sniper should engage moving targets when it is the only option.
Techniques To engage moving targets, the Sniper employs the following techniques:
1) Leading- Engaging moving targets requires the Sniper to place the cross hairs ahead of the target's movement. The distance the cross hairs are placed in front of the target's movement is called a lead. There are four factors in determining leads:
a) Speed of the target - As a target moves faster, it will move a greater distance during the bullet's flight. Therefore, the lead increases as the target's speed increases.
b) Angle of movement - A target moving perpendicular to the bullet's flight path moves a greater lateral distance than a target moving at an angle away from or toward the bullet's path. Therefore, a target moving at a 45 degree angle covers less ground than a target moving at a 90 degree angle.
c) Range to target - The farther away a target is, the longer it takes for the bullet to reach it. Therefore, the lead must be increased as the distance to the target increases.
d) Wind effects - The Sniper must consider how the wind will affect the trajectory of the round. A wind blowing against the target's direction of movement requires less of a lead than a wind blowing in the same direction as the target's movement.
2) Tracking- Tracking requires the Sniper to establish an aiming point ahead of the target's movement and to maintain it as the weapon is fired. This requires the weapon and body position to be moved while following the target and firing.
3) Trapping or Ambushing - Trapping or ambushing is the Sniper's preferred method of engaging moving targets. The Sniper must establish an aiming point ahead of the target and pull the trigger when the target reaches it. This method allows the Sniper's body to remain motionless. With practice, a Sniper can determine exact leads and aiming points using the horizontal stadia lines in the mil dots in the M3A.
4) Firing a snap shot - A Sniper uses this technique to engage a target that only presents itself briefly, then resumes cover. Once he establishes a pattern, he can aim in the vicinity of the targets expected appearance and fire a snap shot at the moment of exposure.
Time of flight ( in seconds ) x target speed ( in feet per seconds / fps ) = lead ( in feet )
then take lead ( in feet ) x .3048 = meters
next meters x 1000 = mil. lead
divided by range
Time of flight
100m = .1 sec / 200m = ..2 / 300m = .4 / 500m = .7 / 600m = .9 / 700m = 1.0 / 800m = 1.3 / 900m = 1.5 / 1000m = 1.8
slow patrol = 1fps / fast patrol = 2fps / slow walk = 4fps / fast walk = 6fps / run = 11fps
It's much better to wait and engage your target when he pauses momentarily rather than attempt a moving target shot. But a moving target may be the only shot you've got. All the data published in the Above Table reflects a target moving 90 degrees to the path of your bullet, that is, moving directly right or left, which is FULL VALUE. Should the target move oblique right or left, whether toward or away from you, use ONE HALF the value since in relative terms he's crossing your front at half the speed. And when he's heading directly toward you or away from you, there's NO VALUE and no movement compensation or leads at all. Aim dead-on.
Last Edit: 23rd Mar 2015 by
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