Reading Wind and Mirage

Last week we discussed how to bore sight and zero your scoped bolt action rifle. In that article, we touched on reading or “doping” the wind, as well as reading mirage. Reading wind and mirage is sometimes mentioned in the same breath as black magic and astrology. But taking cues from the wind and mirage is not so much hocus-pocus. There are some simple techniques for accurately reading the wind and mirage that you can use to determine how these conditions will affect your point of impact.

There are two primary atmospheric conditions that can affect the point of impact of your fired round. The first, and most obvious, is the wind. The wind pushes your bullet as it flies downrange, changing the point of impact. Mirage on the other hand can cause your target to appear blurry and distorted, or even have it appear to be where it is not, such that firing at the apparent image of your target will result in your bullet hitting somewhere other than the intended point of impact. Compensating for wind is fairly easy, even for novice shooters. Mirage on the other hand can be a bit tricky. Almost everyone has seen a mirage before. Look out across a blacktop road on a hot summer day and you’ll see the watery mirage caused by hot air rising off of the sun baked asphalt. This same phenomenon can plague shooters who are engaging targets at long-ranges, even on overcast or mild days. Mirage is caused by differing air densities between the shooter and the target. For an easy example of what mirage does, examine a spoon setting in a tall clear glass of water. When you look at the spoon, you will notice that the handle above the water appears to be in a different place than the handle below the water. This is caused by light being bent as it passes through the boundary between the denser water and the less dense air. In much the same fashion, light reflected off of your target is bent as it passes between dense cool air and less dense hot air. Still, mirage can be your friend, as we’ll discuss later you can use the mirage to your advantage by reading it to get very accurate wind speed estimations.

Wind

The first step in negotiating atmospheric conditions is knowing the wind direction and how much value to assign it. Assessing the direction of the wind is a fairly easy task. Wind flags are used at most long range rifle competitions, and are generally a permanent fixture at established rifle ranges. If your range doesn’t have wind flags you can make some easily and inexpensively using some wooden stakes and fluorescent orange engineers tape. The most basic measurement that a flag is good for is determining actual wind direction. This essential measurement will help you to determine what value to give to the wind; full, three quarters, half, or no value. Wind direction is determined relative to the shooter’s position using the clock face method, or using the angle measured in degrees. When the wind is blowing at 90 degrees (3 o’clock) or 270 degrees (9 o’clock) relative to your shooting position, we assign it a full value of 1. Wind blowing at 45 degrees, 135 degrees, 225 degrees, or 315 degrees relative to your position is given three quarters value. When the wind is blowing at 0 degrees or 180 degrees (12 o’clock or 6 o’clock) relative to your position it is disregarded and given no value. See the diagram to the right for more details on assigning wind value.

Some shooters try to compensate for bullet drop or rise caused by the wind blowing directly away or directly towards the target. In this writer’s opinion, a head or tail wind simply will not affect the bullet flight enough to warrant compensating for. Yes, it is true that a bullet fired into a head wind will drop due to additional aerodynamic drag, but the amount it will drop is almost negligible. At 600 yards, a 150 grain .30-06 bullet will only drop by a half-inch with a 10 mph head wind, a margin of error so small it must be measured in hundredths of a minute of angle (for those doing the math, that’s 1/12th or 0.083 MOA). Only a handful of the most accurate shooters in the world can shoot well enough to be bothered compensating for that small of a drop. If you’re reading this you’re probably not one of them, so don’t worry about it.

Once wind direction and value is determined, it’s time to measure or estimate the wind speed. An anemometer is probably the most accurate device for measuring wind speed, but there are other methods that you can learn. If you find yourself without an anemometer, you can use the guidelines set forth in the Service Rifle Pamphlet produced in 1931 by the US Army Infantry Team. While the information is old, the guideline is as valid today as it was 79 years ago.

0-3 mph Wind hardly felt, but smoke drifts
3-5 mph Wind felt lightly on the face
5-8 mph Leaves are kept in constant movement
8-12 mph Raises dust and loose paper
12-15 mph Causes small trees to sway

Flags can also be used as a rough estimate of wind speed. When observing a normal rectangular flag, estimate the angle between the flag and the pole and divide that number by 4 to get the approximate wind speed. For example, if a flag is flying straight out at a 90 degree angle, the approximate wind speed is 22.5 mph or greater (90/4). If the flag is limp and flapping in a breeze at a 45 degree angle to the pole, the approximate wind speed is 11 to 12 mph. This same estimation method can also be used for streamers and pennants.

As important as knowing how to read the wind is knowing your cartridge and how your load will be affected by various wind speeds. Many novice shooters simply do not understand, or do not believe, how much of an effect a cross wind can have on even the speediest of bullets. Consider a 55 grain .223 round fired down range at over 3,250 FPS for example. With only a modest 5mph cross wind that little .223 bullet will be pushed over 1/2″ off target at only 100 yards. While that might not seem like much, consider that a 10mph wind will result in the same round being pushed more than 1 MOA at any range. Experienced shooters, having been frustrated by wind before, often have the opposite problem and tend to overestimate the effect wind will have on their bullet.

All bullets have a ballistic coefficient that is usually computed by the manufacturer. This number, combined with the flight time of the bullet, can help you determine how much your bullet will be affected by a given wind. By combining the wind direction and value, speed, flight time and the ballistic coefficient of your bullet, you can determine how much to hold over or how much to adjust the windage on your sights. Because of the fact that bullets with differing ballistic coefficients are affected to differing degrees by the wind, there is no hard and fast rule for calculating wind drift. I won’t get into the mathematics of computing wind drift using the ballistic coefficient and flight time of your bullet; wind drift charts and calculators are readily available for almost every cartridge load. Use a wind drift chart for your specific load to determine how much holdover or windage adjustment is necessary.

With the information from the appropriate wind drift chart, apply the wind value to determine the actual drift. For example: Our chart shows that M2 match ammunition for an M1 Garand from American Eagle will drift approximately 5.8 inches at 600 yards with a full value wind at 1 mph. If we actually have a 10 mph wind blowing in at a 45 degree angle (1:30 o’clock) we assign it a value of 3/4 and do the math (5.8 inches X 10 mph X .75) to arrive at 43.5 inches of drift. If the wind shifts to be 30 degrees (1 o’clock) we would assign it a value of 1/2, resulting in 29 inches of drift. Doing the math, we correct approximately 5 MOA for wind at 1/2 value and 6.9 MOA for 3/4 value.


Example of a mirage created by a hot blacktop road; image courtesy of BrentDanley licensed under Creative Commons.

Mirage

Hot air rising up from ground that is warmed by the sun distorts the image of your target, causing it to appear blurry, or even appear to be in a location that it actually is not. This is referred to as mirage. To some degree, heat from the barrel of your rifle can also affect your target image. Eliminating mirage from barrel heat is relatively easy. Many benchrest shooters use extended scope tubes so that the hot air rises around the line of sight, eliminating any blurriness caused by the hot air. Another way to divert the hot air is to tape a light colored piece of cardboard or paper along the top of your barrel.

Mirage caused by hot ground baking in the sun is not possible to eliminate, but it can be understood and worked around. Like the spoon in a glass of water, mirage can cause the image of your target to be higher or lower, but luckily this shift is generally not significant enough to need compensation. For the most part, mirage is only problematic due to the blurriness it imparts to your sight picture. It is in this case that the wind can sometimes be your friend. When looking through your scope across a hot field in calm air the mirage appears to be “boiling” as if peering at your target through a puddle of water. When the wind is blowing however, the mirage will “follow” the wind, in some cases blowing away so that you can get a clear sight picture. Of course, as we mentioned in the section above, you will still need to compensate for the wind. That is where “reading” the mirage comes in. When observing mirage, it often appears as waves running in the direction of the wind. Many people find that reading mirage in this fashion gives a very accurate indication of wind speed. You can actually watch the waves from the mirage as they follow the wind, and estimate the actual wind speed from the speed of the waves.

Reading the mirage in this fashion can be difficult with a headwind or tailwind as those wind conditions can cause the mirage to appear be “boiling” when in actuality it is running with the wind directly away from or towards you. As we stated above however, headwinds and tailwinds generally have only a minimal effect on the overall bullet rise or drop, and for all but the most skilled shooters can be disregarded. Some shooters will even adjust for a boiling mirage in calm conditions as the hot air rising off of the ground can impart a small amount of lift or rise to the bullet. Again, for all but the most skilled shooters this adjustment is not necessary. Any lift from hot air is easily and quickly negated by the force of gravity tugging the bullet downwards at 32 feet per second squared.

When reading mirage to get an idea of wind speed and direction it is important to remember that the mirage you are seeing through your scope is only the first couple of feet in front of your target, as that is the only area that is in focus. The mirage existing the rest of the distance between you and the target is not visible because it is outside the shallow depth of field of your scope. To increase your depth of field, you can narrow the aperture of your scope by placing a lens cover with a tiny hole punched in the middle, effectively stopping down your scope and increasing your depth of field to near infinity. Another method for reducing your aperture size is taping over the objective until there is a small hole between 1/8″ and 1/2″ in diameter. Increasing your field depth in this manner allows you to see shifting winds indicted by the mirage over the total distance between you and the target.

An alternative to this is to change the focus of your scope so that the middle of the distance between you and the target is in focus. By examining the mirage over the total distance between you and the target, small variations in wind direction and speed can be noted and accommodated. While unusual, it is possible to have eddies and even countervailing winds between your firing position and the target. These variances in wind speed and direction will be easy to pick up with a bit of practice studying the mirage at varying distances between you and your target.

Practice Negotiating Wind and Mirage

It is difficult to explain the visual differences between a boil, a mirage running away, or a mirage running towards you. Wind drift is a simple concept to grasp, but it still takes practice to know just how much your particular load will drift. There is really no substitute for actual time spent on the range practicing. You will need to train and practice in order to properly read wind and mirage. On a hot sunny day when the wind is blowing, observe the effect this has on your mirage. With a rifle and scope that have already been zeroed in optimal conditions, take aim at the center of your target and call your shot. Sketch the target in your shooting log and mark the area where you called your shot. When marking your target sketch, be sure to make a note of the conditions in as much detail as possible. Once the range is cold, check your target and compare the point of impact to the called shot on your sketch. Note the differences between the point of aim and the point of impact that the atmospheric conditions have caused. By examining the conditions and the difference between your point of aim and the actual point of impact, you can learn how to best accommodate those situations.

At this point, do not adjust your scope to compensate for the wind or mirage. Instead, hold over the appropriate amount to bring your point of impact to the bullseye of your target. Changing atmospheric conditions can cause you to “chase the wind”, adjusting your scope for conditions that may vary from shot to shot. Take aim at the center of the target. Again, call your shot, mark your target sketch and note where the round actually impacted your target, as well as the observed conditions at the moment of the shot. Repeat this procedure and continue to record information. By taking good notes, you will be able to review your information while not at the range and possibly see things that you might otherwise miss while sitting at the bench.

Repeat this procedure for differing conditions whenever possible. The more information you have, the more you will know how to adjust your point of aim for various conditions.

As with most things in life, there is no replacement for experience when it comes to reading wind and mirage. No amount of explanation can substitute for sitting at a bench and observing how differing atmospheric conditions affect the flight of your bullet. Take what you’ve learned, head out to the range, and see for yourself how long range rifle shooting is affected by wind and mirage. Every range is different and has its own peculiarities, so talk to other shooters and see what you can learn from them about handling wind and mirage.

Keep an eye out next week for our article on compensating for wind and mirage in rifle competitions, where we’ll discuss the tips and tricks used by the pros to keep all of their shots in the X ring under even the most demanding atmospheric conditions.

Estimating Range With A Mil-Dot Reticle

It’s a common feature found on many scopes and other optics, but what exactly is a Mil-Dot reticle, and how do you use it?

It’s important to make clear the distinction between Minutes of Angle and Mils. A Mil, or milliradian is equal to about 3.44 MOA. Most reticles are marked in milliradians using Mil-Dots, while adjustments through the turrets are usually made in fractions of an MOA.

Variable magnification scopes come in two types: First Focal Plane (FFP) or Second Focal Plane (SFP) reticles. Most American scopes have the reticle on the second or rear focal plane, so that the reticle stays the same size as the zoom is changed. European style scopes have the reticle on the first or front focal plane, such that as the magnification on the scope is increased the reticle increases in size. European Mil-Dot reticles are accurate for range estimation at any zoom level. For American style rear focal plane reticles on variable magnification scopes, the Mil-Dot size estimation is only accurate at a certain zoom level. For most variable scopes with a second focal plane reticle the proper magnification is 10x, though this does vary depending on the manufacturer. Consult your owner’s manual to determine what zoom level your Mil-Dot reticle is designed for.


Based on a presumed chest height of 15 inches, this deer would range at approximately 1,389 yards. Too far away for an ethical shot.

The first step in using a Mil-Dot reticle is accurately measuring the size of a target in Mils. Once a target of known size is measured in Mils in the scope, a simple calculation is used to estimate range to the target and compensate for bullet drop. Accurately measuring the target in Mils is not easy, and it is necessary to get an approximation down to around one tenth of a Mil. In the photo shown to the left, the chest of the deer reads at approximately 0.3 Mils. Shown here on the internet, this measurement is fairly easy to see, but when staring down a scope that you are struggling to hold steady at a target that may not be holding still, it becomes much more difficult to get an accurate Mil read.

The formula for computing the estimated range is accomplished by taking the target size in yards, multiplying that by 1000 and then dividing the result by the target measurement in Mils. The result is the approximate distance in yards to the target. The formula for meters is the same, with the target size in meters multiplied by 1000 and divided by the target measurement in Mils giving the approximate range in meters.

So, if you have a man sized target that is six feet tall, you would compute Target size in yards (2) multiplied by 1000 and divided by the measurement in Mils. If a six foot tall target, for example, measures 3 Mils, the formula would be 2 X 1000 / 3= 667 yards.

Size of Target In Yards X 1000 / Mils read = Range to Target (in yards)

The formula is the same for meters:

Size of Target In Meters X 1000 / Mils read = Range to Target (in meters)

There are two ways to compensate for bullet drop. One is to use hold-over. This involves changing the point of aim to be somewhere other than the center of the cross hairs of a scope. The other is to adjust the turrets the appropriate number of clicks until the target can be centered in the cross hairs. Once the range is known, the shooter can then make the necessary adjustments to the elevation using the scope turrets, or hold over the proper amount using the Mil-Dots as an aiming system. If you know your rifle is zeroed at 300 yards for example, your target is an estimated 400 yards and your bullet drop at 400 yards is 15 inches, then you would hold just slightly less than 1 Mil high (1 Mil-Dot is 14.4″ at 400 yards).


Click to download our free Mil-Dot Range Guide (*.PDF)

There are numerous tools on the market that make range estimation using a Mil-Dot system fast and easy. Some use a slide rule type setup where the target size and measurement in Mils is input to the tool, and the range estimate is then shown. Others use a spreadsheet to allow the shooter to quickly find the range estimate. You can download your own “cheat sheet” by clicking on the image shown to the right. Simply save the *.PDF file to your computer and print it out on a plain sheet of 8.5×11 paper. Fold the paper into thirds and cut or tear carefully along the creases and you will have three copies of our Mil-Dot Range Estimation guide you can laminate or simply fold up and take with you.

Here are a few more quick references to help you quickly and easily estimate range using a Mil-Dot reticle: The average adult deer chest is around 18 inches tall.  At 100 yards, that deer chest will take measure 5 Mil-Dots, 2.5 dots at 200 yards, 1.6 dots at 300 yards, and 1.25 dots at 400 yards. For calculating holdover, remember that 1 Mil is about 3.44 MOA, so 1 Mil at 100 yards is about 3.5 inches. At 200 yards, that same Mil is about 7 inches, at 300 a single Mil is 12 inches, and at 400 yards is just over 14 inches.

The only way to get good at using your Mil-Dot reticle to estimate range is to practice. Take a hike and set up multiple targets of known size (1 yard/3 foot squares of poster board on stakes work great) at various distances from your shooting bench. Head back and get out your estimation guide, calculator, or pencil and paper and find your measurements and estimated range. Confirm your estimated range figures with a laser range finder, GPS, or other device. Soon you’ll be able to quickly and easily estimate the range to nearly any target.

Installing an AR-15 Selector and Pistol Grip

Once again we’re continuing our series on assembling your own AR-15 lower receiver. The next step in the process is the installation of the selector, detent and spring, and pistol grip.

To begin the installation, first cock the hammer. Do not let the hammer fall and strike the lower, as it may cause damage.

Insert the selector through the hole in the left side of the receiver.

Flip the receiver over and insert the selector detent with the pointed side toward the selector. Insert the detent spring into the pistol grip. Install the pistol grip onto the receiver. Ensure that the detent spring does not bind as it is placed into the detent hole.

Install the grip screw with washer.

Check the selector for proper operation. Move the selector to safe and pull the trigger. The hammer should not fall. Move the selector to fire and, with your finger over the hammer, pull the trigger. Make sure to catch the hammer as it is sprung forward to prevent it from striking the lower. Keep holding the trigger back and then cock the hammer. It should be engaged by the disconnecter when the trigger is released. Flip the selector back to “safe” and repeat this process.

Helping to Choose A Concealed Carry Handgun For a New Shooter

If you’re a handgun owner and you have friends who are not, you may often find yourself looked to as an expert on the subject. A common question I find myself faced with by new shooters is: “I want to get a handgun for concealed carry and personal protection. What should I get?” It’s a very personal question, with no one right answer. There is a very good reason there is such a broad selection of handguns on the market, and that is that different people look for different qualities in a defensive firearm.

The first thing a new shooter should do is become familiar with pistols in general. One major mistake experienced shooters make is recommending their personal favorite firearm as the gun of choice for a new shooter. I can’t tell you how many times I’ve been at the range and seen a husband encouraging his wife to try out a lightweight .357 Magnum snub nosed revolver. Don’t get me wrong – small hammerless big bore revolvers are carried by thousands of women. Their light weight and small size makes them easy to conceal, and they still pack a wallop. But starting a new shooter off with such a firearm can be a mistake. When dealing with a new shooter, start small by renting something like a Ruger .22 pistol so that they can get used to practicing proper shooting technique. Firearms are intimidating, and starting a newbie off with a fire-belching magnum is a sure-fire way to intimidate them so much that they conclude that they are incapable of handling a firearm.

Once your new shooter is comfortable with a .22, step up and try out a soft shooting .380, 9mm, or .38 Special. Try a wide variety of handguns and let them find out what they like as well as what they don’t like. A shooter looking for their first carry pistol should find one that fits them well. Grip size, grip angle, overall weight and balance, muzzle length, and caliber all play into this complex equation. Be sure to consider the human factor: how intuitively can they manipulate the handguns controls? Is the safety easy to reach? What about the magazine or cylinder release? All of these things contribute to the overall suitability of a pistol to a particular shooter. There’s no set equation for figuring out what pistol fits best – you’ve got to take some for a test drive.

Most pistol ranges have a variety of handguns that can be rented for a small fee. Don’t bother renting full size handguns – these are usually not suitable for concealed carry. Stick with compact and subcompact firearms. Try a variety of actions and calibers. Don’t place too much emphasis on finding a large caliber pistol. While a .357 Sig or .357 Magnum may be your choice as the best carry caliber, it may be a handful for a novice shooter. The ability to maintain consistent and accurate shot placement is far more important than the “stopping power” of any particular caliber. As instructor Greg Hamilton said, “Do you know how to double the effectiveness of any bullet? Put another round through your target.” Two .25 ACP rounds that land solid hits on the target are much more effective than two misses with a .357 Magnum.

Consider also the price and availability of your ammunition. Practice is key to maintaining proficiency with any firearm. Your new shooter may love their .380 subcompact, but with the current ammunition shortage, will they be able to find enough .380 at a reasonable price to practice with? Many pistol models are available in a variety of calibers. If your new shooter falls in love with that Sig 229 in .357 Sig, but you’re concerned with ammo availability, have them try a Sig 229 in .40 S&W instead.

The overall reliability of a handgun is also very important. Many handguns are picky about what type of ammunition they will digest. Ask your local range if you can try some standard pressure defensive rounds through their rental guns. Most ranges will gladly let you give it a test drive if you purchase the ammunition there (most will not let you run +P high pressure rounds). In addition to their ability to feed ammunition, some firearms are simply more reliable than others. Talk to an experienced shooter or range master about the reliability of the pistol your new shooter is considering for purchase. Pistols that are carried regularly are exposed to all manner of fouling media. Lint, dirt, and dust can collect on the pistol, and rust can be an issue in high humidity environments or during the summer. Some handguns are simply better suited for concealed carry. Look for polymer, stainless steel, or other frames that will resist moisture, dirt, and dust.

Once a new shooter has settled on what gun is right, the pocket book comes into play. Firearms are not cheap as a general rule, and it’s possible to find that the right pistol for your new shooter is out of their budget. If that is the case, talk to your local firearm dealer about layaway plans, or consider buying used. Many manufacturers like Sig Sauer offer factory certified used firearms that come with an excellent warranty and are priced at a significant discount. If a factory certified used firearm isn’t a possibility, have a gunsmith inspect the potential purchase. They can spot excessive wear and abuse and can tell how well a used handgun has been cared for.

Finally, once the new purchase has been made, practice! Practice is critical to being able to properly employ a firearm in a self defense situation, so continue to encourage a new shooter to accompany you to the range and practice with their new pistol. If they’ve chosen a handgun that suits them well, practice will be an enjoyable pastime that the two of you can spend together.

Reloading – A Beginner’s Guide – Part 1

Ammunition prices continued to rise and show no sign of falling anytime soon. Even prices for primers, brass and bullets have gone up significantly. So, what’s a shooter to do? For myself and others, reloading is one solution.

Reloading involves recycling spent brass and prepping it to reload with new primers, powder, and bullets. But where do you begin?

Cleaning Your Molle Gear

You’ve got the gear, you’ve assembled your kit, gone out into the field, and now you’re back, and your gear is covered with all manner of dirt, mud, leaves and brush. How do you safely clean your MOLLE gear?

Red dummy bullet

Dry-Fire Training at Home

I recently shot a local IDPA (International Defensive Pistol Association) match. I did OK but noticed a couple of problems that slowed me down significantly—namely, quickly and smoothly drawing from the holster and pressing forward to the target.