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Tuesday, January 10, 2012

Scope Reticles 101 Chapter 2

    Previously we covered basic and illuminated style reticles. This time let’s look at the bullet drop compensator and ranging reticles. Both give the shooter more information than the basic reticles and some of these are illuminated as well.     First the bullet drop compensator style reticles (BDC). These scopes are designed to zero the weapon system at a specified distance and use the BDC to adjust for longer shots. These recticles can be caliber specific. The key point here is to read the manufactures directions on how to use the reticle. They will vary. Some scope builders group calibers into different classes based on velocity of the cartridge. This makes the reticle appeal to a broad market base. These work well on large targets. The variances in weather and caliber ballistics make it hard to hit a smaller target. The turrets on these scopes vary as well. Most are not numbered since they are designed to be set and left alone. Newer versions of the BDC have marks for wind corrections. These windage marks are set at 5 or 10 mph. This means the shooter must estimate the correction for wind values that are different than the set value. Remember the wind velocity and the direction/angle are important factors in making corrections. Some of these reticles have so many lines in the scope they are hard to read clearly. Making a quick shot or a fast follow up shot is difficult when you need to pause to comprehend all the different marks on the reticle. You can use the BDC reticle for ranging in a similar fashion as the duplex reticle. The shooter must practice ranging targets and build a data card for this method to work. This type of reticle is not as precise as the Mil-dot or MOA style.     Mil Radian scopes are based on the angular relationship of a circle and it’s radius. It was first used by artillery crews to aim the big guns over great distances. The term Mil dots was adapted since the mil radian is used and dots are placed on the crosshairs 1 mil-radian apart. The first scopes used perfectly round dots. The USMC version uses small ovals in place of the dots. Later versions use hash marks at each mil radian and some reticles have hash marks at 0.5 mil or even 0.2 mil.  A mil radian is approx. 3.6 inches at 100 yards or 36 inches at 1000 yards. Some manufactures are using minute of angle (MOA) instead of mils: 1 MOA is 1 inch at 100 and 10 inches at 1000. The scopes I have used were all graduated in 2 MOA not 1 MOA.  As a comparison at 500 yards 1 mil is 18 inches and 2 moa would be 10 inches. Most scope turrets are divided into segments of MOA. The most common is ¼ MOA per click, or ¼ inch at 100 yards.  This works very well when the reticle is in MOA also. Just recently scope manufactures offered scopes with turrets that are set in Mil radian adjustments. The most common is 1/10th mil radian. This computes to 0.36 inches per click of the turrets at 100 yards. Scopes with mil radian reticles and MOA turrets have to have the corrections converted to inches then to moa to make the corrections. If the turrets and reticle are in the same dimensions there is no conversion. The shooter simply reads the correction from the reticle and turns the dial.    Here is an example. The shooter misses a target by 1 mil as observed through the scope. They would just rotate the turret 10 clicks to make the correction. If the turrets were in MOA he must convert 1 mil to inches. At 200 yards that would be 7.2 inches, now the shooter must move the turret to correct for 7.2 inches. The 7.2 inches is converted to clicks by dividing 7.2 by ½ inch since 1 click is equal to ½” at 200 yards. The result is 14 clicks. 14x1/2 = 7. Since there are no half clicks on the scope we round off to the nearest whole number.
     Range estimation with a mil radian scope is easier than most other reticle types. Since we know the size of the target and the mil radian is obtained through the scope we can calculate the distance to the target. The formula is size of target in inches multiplied by 27.77. (This is a fixed number in the formula.) The result is divided by number of mils. This gives you the distance. The accuracy of this method depends on how accurate you read the mils from the scopes reticle. A 2/10ths of a mil misread will throw the range estimation off enough to miss the target. This is why most ranging should be done with the scope on the highest power setting. The MOA recticles are used the same way with the constant in the formula as 95.5.  Remember there are imported scopes that look like they have a mil dot reticle but reading the fine print reveals they are for reference only and aren’t true mil dots. It is easy to check by drawing a box on a piece of blank paper. Make it 7.2 inches tall and 3.6inches wide. Set it at 100 yards and observe it thru your scope it should be 2 mils tall and 1 mil wide. This same exercise will tell you on what power the scope should be for ranging. Front focal plane scopes should be accurate at any power while rear focal plane scopes normally must be set on the highest power to range a target. There are a few that must be set on 1 specific power setting to be accurate. Again, read the manufacturer’s directions.     Optics manufacturers are now making rifle scopes, binoculars and spotting scopes  with the same reticles. This is a great improvement for the shooter/ spotter team/ the spotter simply calls the correction directly from what he sees through the spotting scope. The shooter then holds off the correction and makes another shot. If time permits the shooter can dial in the correction to scope on the turrets that are matched to the scope reticle. An experienced shooter can adjust the turrets without looking at them     Horrus now has scopes with a mil-radian grid system just below the stadia lines in their scopes. Each mark is 0.2 mils apart. The idea behind this is to allow the shooter to count the marks to improve ranging. It also allows for instant wind correction for a miss or hold over for distance correction. I have only used the grid system a few times and it was confusing and time consuming. I need more practice on this reticle. The one drawback was the additional cost to have this reticle in the scope. Leupold offers this option in a few Mark 4 scope models.     In the past twenty years scope manufactures have combined features on scopes to give the shooters better choices. The new models really do combine the best features of illumination and cross hair reticles. Several companies offer illuminated recticles with BDC or Mil-dots. Trijicon has fixed power scopes with a fiber optic aiming point and a BDC below it. They also have a Mil dot scope with a fiber optic center dot. Leupold has the fire dot scopes and illuminated TMR reticle.     I used an illuminated TMR in 2-8x36 on a 20’ AR for the Mammoth Sniper challenge. One stage was on the side of a mountain under a full canopy of hardwoods on a rainy day. The targets were scattered through the woods downhill from the shooter. During the walk through I noticed how dark it was and how the trees and limbs looked black since they were wet. The targets were all steel and grey in color. I turned on the illuminated reticle and went 5 for 5 on that stage. It was my best stage of the match.     The new trend is to mount 2 optics on rifles, one variable power scope in the standard position and a red dot style at the 1 O/C position. This gives the shooter the option of making a long range shot or a CQB type shot with the same rifle by tilting the rifle to the left. I just learned of a new scope, designed for the military, that is 1.1-8 power. The only drawback I see is the $3800.00 price tag. You can shoot CQB with a magnified optic.  Shooting long range with a non-magnified red dot is nearly impossible.        Just remember under 200 yards the options are wide open. At 200 – 600 yards the choices become limited simply because you can’t hit what you can’t see. At distances over 600 yards the quality of glass and the turrets make a big difference if you want to hit what you see. Remember to practice with your weapon system and build your data book and range card. This will improve your shooting tremendously and you won’t have to relearn the dope from the previous training session.

Scott Vandiver

SI Staff Instructor Georgia

www.centerfiretraining.com

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The Suarez International Blog is a "warrior lifestyle" publication dedicated to the modern excellence-seeking martial enthusiast. Every article and video will feature the most up to date weapons, tactics, technology, and training methods available today. Not limited to merely "guns", we include articles on international adventure travel, extreme physical training, and living well in the modern world.