Any long range shooter knows that wind is our ultimate nemesis. The best ways of overcoming wind are to measure what we can and use computers to calculate deflection. The Applied Ballistics Kestrel is a great tool for this. As good as our tools may be, we don’t always have them at our fingertips, or they break, batteries go dead, and so on. In these cases, it’s nice to have a simple way of estimating wind based on known variables. There are numerous wind formulas of various complexity.
The Applied Ballistics (AB) Wind Hack is about the simplest way to get a rough wind solution. Here it is: You simply add 2 to the first digit of your G7 BC, and divide your drop by this number to get the 10 mph crosswind deflection. For example, suppose you’re shooting a .308 caliber 175-grain bullet with a G7 BC of 0.260 at 1000 yards, and your drop is 37 MOA. For a G7 BC of 0.260, your “wind number” is 2+2=4. So your 10 mph wind deflection is your drop (37 MOA) divided by your “wind number” (4) = 9.25 MOA. This is really close to the actual 9.37 MOA calculated by the ballistic software.
WIND HACK Formula
10 mph Cross Wind Deflection = Drop (in MOA) divided by (G7 BC 1st Digit + 2)
Give the AB wind hack a try to see how it works with your ballistics!
Some Caveats: Your drop number has to be from a 100-yard zero. This wind hack is most accurate for supersonic flight. Within supersonic range, accuracy is typically better than +/-6″. You can easily scale the 10 mph crosswind deflection by the actual wind speed. Wind direction has to be scaled by the cosine of the angle.
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“A bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.”
A few seasons back a good friend ventured to the high country of Colorado to pursue elk. He recently zeroed his rifle in California, at a range just a few hundred feet Above Mean Sea Level (AMSL). He wondered if the higher altitude in Colorado could alter his ballistics. The answer is a definite yes. However the good news is that free ballistics calculators can help you plot reliable drop charts for various shooting locations, high or low.
The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:
“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ AMSL (Above Mean Sea Level) or less. I’ll need about 29-30 MOA to get from 100 yards to 1000 yards with a Berger 155gr VLD at 2960 fps. By contrast, in Raton, NM, located at 6600′ AMSL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”
As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect. It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet AMSL), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestrel, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.
To learn more about all aspects of Exterior Ballistics, Hornady has a useful discussion of External Ballistics including the effects of altitude and temperature. To dig deeper, Sierra Bullets has a comprehensive Exterior Ballistics Resource Page with multiple sections from the Sierra Manual (4th and 5th Editions), including:
Example from Section 3.0: “When a bullet flies through the air, two types of forces act on the bullet to determine its path (trajectory) through the air. The first is gravitational force; the other is aerodynamics. Several kinds of aerodynamic forces act on a bullet: drag, lift, side forces, Magnus force, spin damping force, pitch damping force, and Magnus cross force. The most important of these aerodynamic forces is drag. All the others are very small in comparison when the bullet is spin-stabilized.”
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Want to learn more about Long Range Shooting? Check out the NSFF “Elements of Long Range Shooting” videos hosted by ballistics guru Bryan Litz of Applied Ballistics. In this multi-part series, Bryan covers a variety of topics of interest to precision shooters. For today’s Saturday at the Movies special, we feature seven of Bryan’s videos. Watch other informative Long Range Shooting and Ballistics videos with Bryan Litz on the NSSF YouTube Channel.
Atmospherics and Density Altitude
Bryan Litz explains: “An important element in calculating an accurate firing solution for long-range shooting is understanding the effects of atmospherics on a projectile.” Atmospherics include air pressure, air temperature, and humidity. Bryan notes: “Temperature, pressure, and humidity all affect the air density… that the bullet is flying through. You can combine all those factors into one variable called ‘Density Altitude’.” Density Altitude is used by the ballistic solver to account for variables that affect bullet flight.
Bullet Ballistic Coefficients
A bullet’s ballistic coefficient (BC) basically expresses how well the bullet flies through the air. Higher BC bullets have less aerodynamic drag than lower BC projectiles. You will see BCs listed as either G1 and G7 numbers. These correspond to different bullet shape models. Generally speaking, the G7 model works better for the long, boat-tail bullets used for long-range shooting. Notably, a bullet’s drag is NOT constant in flight. The true BC can vary over the course of the trajectory as the bullet velocity degrades. In other words, “BC is dynamic”. That said, you can make very accurate drop charts using the BCs provided by major bullet-makers, as plugged into solvers. However, long-range competitors may want to record “real world” drop numbers at various distances. For example, we’ve seen trajectories be higher than predicted at 500 yards, yet lower than predicted at 1000.
Transonic Range
When considering your rifle’s long-range performance, you need to understand the limit of your bullet’s supersonic range. As the bullet slows below the speed of sound, it enters the transonic zone. This can be accompanied by variations in stability as well as BC changes. Bryan explains “once your bullet slows done below supersonic and you get into transonic effects, there are a lot more considerations that come into play. The drag of the bullet becomes less certain, the stability of the bullet can be challenged, and things related to long times of flight, such as Coriolis and Spin Drift, come into play. So whenever you are shooting long range you need to where your bullet slows down to about 1340 fps.”
Ballistics Solvers — Many Options
Bryan Litz observes: “When we talk about the elements of long range shooting, obviously a very important element is a getting a fire solution, using a ballistic solver. There are a lot of ballistic solvers out there… Applied Ballistics has smartphone Apps. Applied Ballistics has integrated the ballistic solver directly into a Kestral, and the same solver runs (manually) on the Accuracy Solutions Wiz-Wheel. The point is, if it is an Applied Ballistics device it is running the same solutions across the board.”
Bullet Stability and Twist Rates
In this video, Bryan Litz talks about bullet in-flight stability and how to calculate barrel twist-rate requirements for long-range bullets. Bryan explains that bullet stability (for conventional projectiles) is basically provided by the spinning of the bullet. But this spin rate is a function of BOTH the nominal twist rate of the barrel AND the velocity of the projectile. Thus, when shooting the same bullet, a very high-speed cartridge may work with a slower barrel twist rate than is required for a lower-speed (less powerful) cartridge. For match bullets, shot at ranges to 1000 yards and beyond, Bryan recommends a twist rate that offers good stability.
Scope Tracking — Tall Target Test
Have you recently purchased a new scope? Then you should verify the actual click value of the turrets before you use the optic in competition. While a scope may have listed click values of 1/4-MOA, 1/8-MOA or 0.1 Mils, the reality may be slightly different. Many scopes have actual click values that are slightly higher or lower than the value claimed by the manufacturer. The small variance adds up when you click through a wide range of elevation. In this video, Bryan Litz shows how to verify your true click values using a “Tall Target Test”. The idea is to start at the bottom end of a vertical line, and then click up 30 MOA or so. Multiply the number of clicked MOA by 1.047 to get the claimed value in inches. For example, at 100 yards, 30 MOA is exactly 31.41 inches. Then measure the difference in your actual point of impact.
Coriolis Effect
The Coriolis Effect comes into play with extreme long-range shots. The rotation of the earth actually moves the target a small distance (in space) during the long duration of the bullet’s flight. Bryan Litz notes that, in most common shooting situations inside 1K, Coriolis is not significant. At 1000 yards, the Effect represents less than one click (for most cartridge types). Even well past 1000 yards, in windy conditions, the Coriolis Effect may well be “lost in the noise”. But in very calm conditions, when shooting at extreme ranges, Bryan says you can benefit from adjusting your ballistics solution for Coriolis: “The Coriolis Effect… has to do with the spin of the earth. The consequence of that is that, if the flight time of the bullet gets significantly long, the bullet can have an apparent drift from its intended target. The amount [of apparent drift] is very small — it depends on your latitude and azimuth of fire on the planet.”
About Bryan Litz
Bryan began his career as a rocket scientist, quite literally. He then started Applied Ballistics, the leading company focusing on ballistics science for rifle shooting. A past F-TR Long-Range National Champion and Chief Ballistician for Berger Bullets, knows his stuff. His Applied Ballistics squad was the winning team at the 2017 King of 2 Miles event, and Applied Ballistics has earned major U.S. defense contracts.
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A Kestrel Wind Meter will record wind speed with its impeller wheel. However, to get the most accurate wind velocity reading, you need to have your Kestrel properly aligned with the wind direction. To find wind direction, first orient the Kestrel so that the impeller runs at minimal speed (or stops), and only then turn the BACK of the Kestrel into the wind direction. Do NOT simply rotate the Kestrel’s back panel looking for the highest wind speed reading — that’s not the correct method for finding wind direction. Rotate the side of the Kestrel into the wind first, aiming for minimal impeller movement. The correct procedure is explained below by the experts at Applied Ballistics.
How to Find the Wind Direction with a Kestrel Wind Meter
Here is the correct way to determine wind direction with a Kestrel wind meter when you have no environmental aids — no other tools than a Kestrel. (NOTE: To determine wind direction, a mounted Wind Vane is the most effective tool, but you can also look at flags, blowing grass, or even the lanyard on your Kestrel).
Step 1: Find the wind’s general direction.
Step 2: Rotate the Wind Meter 90 degrees, so that the wind is impacting the side (and not the back) of the wind meter, while still being able to see the impeller.
Step 3: Fine-tune the direction until the impeller drastically slows, or comes to a complete stop (a complete stop is preferred). If the impeller won’t come to a complete stop, find the direction which has the lowest impact on the impeller.
Step 4: Turn the BACK of the Kestrel towards the direction from which the wind is blowing. Then press the capture button, and record your wind speed.
Do NOT simply point the Kestrel’s back into the wind until you get the highest wind speed — that’s not the correct method.
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Kestrel wind and weather meters are often regarded as the best on the market — for good reason. Here are a series of three videos by F-Class John that show how the Kestrel 5700 with Elite Ballistics works. This article reviews the advanced Kestrel 5700 Elite Wind Meter with sophisticated ballistics capabilities. Our review features three videos by F-Class John that show how the Kestrel 5700 Elite functions with Applied Ballistics APP software and LiNK connection.
This Part I Video starts with a basic Kestrel Anemometer (blue case, 00:00-00:40) wind meter. Then reviewer F-Class John looks at the “smart” Kestrel 5700 with Elite Ballistics. John explains the many features of the Kestrel 5700 and how it holds a powerful ballistics calculator in the convenient, easy-to-tote Kestrel package. With Elite Ballistics, once you enter data about your bullets, velocity, zero, and rifle, the Kestrel can calculate come-ups and wind corrections. If you don’t yet own a Kestrel, we highly recommend you watch this series of videos that explains advanced Kestrel features in detail.
This Part II Video shows the key features of the advanced software APP used by the Kestrel 5700 unit with Elite Ballistics. The Kestrel 5700 can “talk” to a mobile device that runs the Applied Ballistics software APP that contains bullet databases and allows you to enter key information such as muzzle velocity, bullet BC, zero distance, velocity, wind, and environmental factors (altitude, temperature etc.). There are also gun-specific factors such as scope height over bore and barrel twist rate. The video also explains how “range cards” are created and how to view them with your Elite Ballistics-enabled Kestrel. John notes: “The APP is great because you don’t have to fiddle with the Kestrel’s buttons. It’s much easier to enter data and change settings with the APP.”
This Part III video shows how to determine true wind direction by aligning the SIDE of the unit into the wind. You essentially want to set the unit 90 degrees to the wind direction so the impeller runs as slowly as possible. Then, after you set your target distance (See 3:03), the unit can give you precise come-ups for your intended target (10.28 MOA for 559 yards here). The Kestrel then calculates the cross-wind correction as well (See 3:12).
DISCLAIMER: This video and description contains affiliate links, which means that if you click on one of the product links, the video author may receive a small commission. This helps support F-Class John’s YouTube channel and allows him to continue to make videos like this.
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“A bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.”
It’s hunting season, and we have a friend who wants to go the high country of Colorado to pursue elk. He recently zeroed his rifle in California, at a range just a few hundred feet Above Mean Sea Level (AMSL). He wondered if the higher altitude in Colorado could alter his ballistics. The answer is a definite yes. However the good news is that free ballistics calculators can help you plot reliable drop charts for various shooting locations, high or low.
The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:
“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ AMSL (Above Mean Sea Level) or less. I’ll need about 29-30 MOA to get from 100 yards to 1000 yards with a Berger 155gr VLD at 2960 fps. By contrast, in Raton, NM, located at 6600′ AMSL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”
As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect. It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet AMSL), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestrel, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.
To learn more about all aspects of Exterior Ballistics, Hornady has a useful discussion of External Ballistics including the effects of altitude and temperature. To dig deeper, Sierra Bullets has a comprehensive Exterior Ballistics Resource Page with multiple sections from the Sierra Manual (4th and 5th Editions), including:
Example from Section 3.0: “When a bullet flies through the air, two types of forces act on the bullet to determine its path (trajectory) through the air. The first is gravitational force; the other is aerodynamics. Several kinds of aerodynamic forces act on a bullet: drag, lift, side forces, Magnus force, spin damping force, pitch damping force, and Magnus cross force. The most important of these aerodynamic forces is drag. All the others are very small in comparison when the bullet is spin-stabilized.”
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Kestrel wind and weather meters are often regarded as the best on the market — for good reason. Here are a series of three videos by F-Class John that show how the Kestrel 5700 with Elite Ballistics works. This article reviews the advanced Kestrel 5700 Elite Wind Meter with sophisticated ballistics capabilities. Our review features three videos by F-Class John that show how the Kestrel 5700 Elite functions with Applied Ballistics APP software and LiNK connection.
This Part I Video starts with a basic Kestrel Anemometer (blue case, 00:00-00:40) wind meter. Then reviewer F-Class John looks at the “smart” Kestrel 5700 with Elite Ballistics. John explains the many features of the Kestrel 5700 and how it holds a powerful ballistics calculator in the convenient, easy-to-tote Kestrel package. With Elite Ballistics, once you enter data about your bullets, velocity, zero, and rifle, the Kestrel can calculate come-ups and wind corrections. If you don’t yet own a Kestrel, we highly recommend you watch this series of videos that explains advanced Kestrel features in detail.
This Part II Video shows the key features of the advanced software APP used by the Kestrel 5700 unit with Elite Ballistics. The Kestrel 5700 can “talk” to a mobile device that runs the Applied Ballistics software APP that contains bullet databases and allows you to enter key information such as muzzle velocity, bullet BC, zero distance, velocity, wind, and environmental factors (altitude, temperature etc.). There are also gun-specific factors such as scope height over bore and barrel twist rate. The video also explains how “range cards” are created and how to view them with your Elite Ballistics-enabled Kestrel. John notes: “The APP is great because you don’t have to fiddle with the Kestrel’s buttons. It’s much easier to enter data and change settings with the APP.”
This Part III video shows how to determine true wind direction by aligning the SIDE of the unit into the wind. You essentially want to set the unit 90 degrees to the wind direction so the impeller runs as slowly as possible. Then, after you set your target distance (See 3:03), the unit can give you precise come-ups for your intended target (10.28 MOA for 559 yards here). The Kestrel then calculates the cross-wind correction as well (See 3:12).
DISCLAIMER: This video and description contains affiliate links, which means that if you click on one of the product links, the video author may receive a small commission. This helps support F-Class John’s YouTube channel and allows him to continue to make videos like this.
Share the post "How to Use a Kestrel with Applied Ballistics Software"
“A bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.”
Last month a good friend ventured to the high country of Colorado to pursue elk. He recently zeroed his rifle in California, at a range just a few hundred feet Above Mean Sea Level (AMSL). He wondered if the higher altitude in Colorado could alter his ballistics. The answer is a definite yes. However the good news is that free ballistics calculators can help you plot reliable drop charts for various shooting locations, high or low.
The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:
“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ AMSL (Above Mean Sea Level) or less. I’ll need about 29-30 MOA to get from 100 yards to 1000 yards with a Berger 155gr VLD at 2960 fps. By contrast, in Raton, NM, located at 6600′ AMSL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”
As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect. It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet AMSL), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestrel, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.
To learn more about all aspects of Exterior Ballistics, Hornady has a useful discussion of External Ballistics including the effects of altitude and temperature. To dig deeper, Sierra Bullets has a comprehensive Exterior Ballistics Resource Page with multiple sections from the Sierra Manual (4th and 5th Editions), including:
Example from Section 3.0: “When a bullet flies through the air, two types of forces act on the bullet to determine its path (trajectory) through the air. The first is gravitational force; the other is aerodynamics. Several kinds of aerodynamic forces act on a bullet: drag, lift, side forces, Magnus force, spin damping force, pitch damping force, and Magnus cross force. The most important of these aerodynamic forces is drag. All the others are very small in comparison when the bullet is spin-stabilized.”
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Any long range shooter knows that wind is our ultimate nemesis. The best ways of overcoming wind are to measure what we can and use computers to calculate deflection. The Applied Ballistics Kestrel is a great tool for this. As good as our tools may be, we don’t always have them at our fingertips, or they break, batteries go dead, and so on. In these cases, it’s nice to have a simple way of estimating wind based on known variables. There are numerous wind formulas of various complexity.
The Applied Ballistics (AB) Wind Hack is about the simplest way to get a rough wind solution. Here it is: You simply add 2 to the first digit of your G7 BC, and divide your drop by this number to get the 10 mph crosswind deflection. For example, suppose you’re shooting a .308 caliber 175-grain bullet with a G7 BC of 0.260 at 1000 yards, and your drop is 37 MOA. For a G7 BC of 0.260, your “wind number” is 2+2=4. So your 10 mph wind deflection is your drop (37 MOA) divided by your “wind number” (4) = 9.25 MOA. This is really close to the actual 9.37 MOA calculated by the ballistic software.
WIND HACK Formula
10 mph Cross Wind Deflection = Drop (in MOA) divided by (G7 BC 1st Digit + 2)
Give the AB wind hack a try to see how it works with your ballistics!
Some Caveats: Your drop number has to be from a 100-yard zero. This wind hack is most accurate for supersonic flight. Within supersonic range, accuracy is typically better than +/-6″. You can easily scale the 10 mph crosswind deflection by the actual wind speed. Wind direction has to be scaled by the cosine of the angle.
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Want to learn more about Long Range Shooting? Check out the NSFF “Elements of Long Range Shooting” videos hosted by ballistics guru Bryan Litz of Applied Ballistics. In this multi-part series, Bryan covers a variety of topics of interest to precision shooters. For today’s Saturday at the Movies special, we feature seven of Bryan’s videos. Watch other informative Long Range Shooting and Ballistics videos with Bryan Litz on the NSSF YouTube Channel.
Atmospherics and Density Altitude
Bryan Litz explains: “An important element in calculating an accurate firing solution for long-range shooting is understanding the effects of atmospherics on a projectile.” Atmospherics include air pressure, air temperature, and humidity. Bryan notes: “Temperature, pressure, and humidity all affect the air density… that the bullet is flying through. You can combine all those factors into one variable called ‘Density Altitude’.” Density Altitude is used by the ballistic solver to account for variables that affect bullet flight.
Bullet Ballistic Coefficients
A bullet’s ballistic coefficient (BC) basically expresses how well the bullet flies through the air. Higher BC bullets have less aerodynamic drag than lower BC projectiles. You will see BCs listed as either G1 and G7 numbers. These correspond to different bullet shape models. Generally speaking, the G7 model works better for the long, boat-tail bullets used for long-range shooting. Notably, a bullet’s drag is NOT constant in flight. The true BC can vary over the course of the trajectory as the bullet velocity degrades. In other words, “BC is dynamic”. That said, you can make very accurate drop charts using the BCs provided by major bullet-makers, as plugged into solvers. However, long-range competitors may want to record “real world” drop numbers at various distances. For example, we’ve seen trajectories be higher than predicted at 500 yards, yet lower than predicted at 1000.
Transonic Range
When considering your rifle’s long-range performance, you need to understand the limit of your bullet’s supersonic range. As the bullet slows below the speed of sound, it enters the transonic zone. This can be accompanied by variations in stability as well as BC changes. Bryan explains “once your bullet slows done below supersonic and you get into transonic effects, there are a lot more considerations that come into play. The drag of the bullet becomes less certain, the stability of the bullet can be challenged, and things related to long times of flight, such as Coriolis and Spin Drift, come into play. So whenever you are shooting long range you need to where your bullet slows down to about 1340 fps.”
Ballistics Solvers — Many Options
Bryan Litz observes: “When we talk about the elements of long range shooting, obviously a very important element is a getting a fire solution, using a ballistic solver. There are a lot of ballistic solvers out there… Applied Ballistics has smartphone Apps. Applied Ballistics has integrated the ballistic solver directly into a Kestral, and the same solver runs (manually) on the Accuracy Solutions Wiz-Wheel. The point is, if it is an Applied Ballistics device it is running the same solutions across the board.”
Bullet Stability and Twist Rates
In this video, Bryan Litz talks about bullet in-flight stability and how to calculate barrel twist-rate requirements for long-range bullets. Bryan explains that bullet stability (for conventional projectiles) is basically provided by the spinning of the bullet. But this spin rate is a function of BOTH the nominal twist rate of the barrel AND the velocity of the projectile. Thus, when shooting the same bullet, a very high-speed cartridge may work with a slower barrel twist rate than is required for a lower-speed (less powerful) cartridge. For match bullets, shot at ranges to 1000 yards and beyond, Bryan recommends a twist rate that offers good stability.
Scope Tracking — Tall Target Test
Have you recently purchased a new scope? Then you should verify the actual click value of the turrets before you use the optic in competition. While a scope may have listed click values of 1/4-MOA, 1/8-MOA or 0.1 Mils, the reality may be slightly different. Many scopes have actual click values that are slightly higher or lower than the value claimed by the manufacturer. The small variance adds up when you click through a wide range of elevation. In this video, Bryan Litz shows how to verify your true click values using a “Tall Target Test”. The idea is to start at the bottom end of a vertical line, and then click up 30 MOA or so. Multiply the number of clicked MOA by 1.047 to get the claimed value in inches. For example, at 100 yards, 30 MOA is exactly 31.41 inches. Then measure the difference in your actual point of impact.
Coriolis Effect
The Coriolis Effect comes into play with extreme long-range shots. The rotation of the earth actually moves the target a small distance (in space) during the long duration of the bullet’s flight. Bryan Litz notes that, in most common shooting situations inside 1K, Coriolis is not significant. At 1000 yards, the Effect represents less than one click (for most cartridge types). Even well past 1000 yards, in windy conditions, the Coriolis Effect may well be “lost in the noise”. But in very calm conditions, when shooting at extreme ranges, Bryan says you can benefit from adjusting your ballistics solution for Coriolis: “The Coriolis Effect… has to do with the spin of the earth. The consequence of that is that, if the flight time of the bullet gets significantly long, the bullet can have an apparent drift from its intended target. The amount [of apparent drift] is very small — it depends on your latitude and azimuth of fire on the planet.”
About Bryan Litz
Bryan began his career as a rocket scientist, quite literally. He then started Applied Ballistics, the leading company focusing on ballistics science for rifle shooting. A past F-TR Long-Range National Champion and Chief Ballistician for Berger Bullets, knows his stuff. His Applied Ballistics squad was the winning team at the 2017 King of 2 Miles event, and Applied Ballistics has earned major U.S. defense contracts.
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“A bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.”
It’s hunting season, and a good friend is heading to the high country of Colorado next week to pursue elk. He recently zeroed his rifle in California, at a range just a few hundred feet Above Mean Sea Level (AMSL). He wondered if the higher altitude in Colorado could alter his ballistics. The answer is a definite yes. However the good news is that free ballistics calculators can help you plot reliable drop charts for various shooting locations, high or low.
The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:
“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ AMSL (Above Mean Sea Level) or less. I’ll need about 29-30 MOA to get from 100 yards to 1000 yards with a Berger 155gr VLD at 2960 fps. By contrast, in Raton, NM, located at 6600′ AMSL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”
As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect. It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet AMSL), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestrel, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.
To learn more about all aspects of Exterior Ballistics, Hornady has a useful discussion of External Ballistics including the effects of altitude and temperature. To dig deeper, Sierra Bullets has a comprehensive Exterior Ballistics Resource Page with multiple sections from the Sierra Manual (4th and 5th Editions), including:
Example from Section 3.0: “When a bullet flies through the air, two types of forces act on the bullet to determine its path (trajectory) through the air. The first is gravitational force; the other is aerodynamics. Several kinds of aerodynamic forces act on a bullet: drag, lift, side forces, Magnus force, spin damping force, pitch damping force, and Magnus cross force. The most important of these aerodynamic forces is drag. All the others are very small in comparison when the bullet is spin-stabilized.”
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The 2021 NRA F-Class National Championships are underway right now at Camp Atterbury, Indiana. The Mid-Range Nationals concluded yesterday with the Team Match, and the Long-Range F-Class Nationals commence today, July 27, 2021 and run through Friday, July 30th. For F-Class competitors, making the right wind call is a vital skill. Many shooters and team wind coaches will be using Kestrel Wind Meters, widely regarded as the best on the market.
This article reviews the advanced Kestrel 5700 Elite Wind Meter with sophisticated ballistics capabilities. Our review features three videos by F-Class John that show how the Kestrel 5700 Elite works with Applied Ballistics APP software and LiNK connection.
This Part I Video starts with a basic Kestrel Anemometer (blue case, 00:00-00:40) wind meter. Then reviewer F-Class John looks at the “smart” Kestrel 5700 Elite with Applied Ballistics functionality and LiNK Bluetooth connectivity. John explains the many features of the Kestrel 5700 and how it holds a powerful ballistics calculator in the convenient, easy-to-tote Kestrel package. With the Kestrel 5700 Elite, once you enter data about your bullets, velocity, zero, and rifle, the Kestrel can calculate come-ups and wind corrections. If you don’t yet own a Kestrel, we highly recommend you watch this series of videos that explains advanced Kestrel features in detail.
This Part II Video shows the key features of the advanced software APP used by the Kestrel 5700 Elite unit with Applied Ballistics. The Kestrel 5700 can “talk” to a mobile device that runs the Applied Ballistics software APP that contains bullet databases and allows you to enter key information such as muzzle velocity, bullet BC, zero distance, velocity, wind, and environmental factors (altitude, temperature etc.). There are also gun-specific factors such as scope height over bore and barrel twist rate. The video also explains how “range cards” are created and how to view them with your Elite Ballistics-enabled Kestrel. John notes: “The APP is great because you don’t have to fiddle with the Kestrel’s buttons. It’s much easier to enter data and change settings with the APP.”
This Part III video shows how to determine true wind direction by aligning the SIDE of the unit into the wind. You essentially want to set the unit 90 degrees to the wind direction so the impeller runs as slowly as possible. Then, after you set your target distance (See 3:03), the unit can give you precise come-ups for your intended target (10.28 MOA for 559 yards here). The Kestrel then calculates the cross-wind correction as well (See 3:12).
DISCLAIMER: This video and description contains affiliate links, which means that if you click on one of the product links, the video author may receive a small commission. This helps support F-Class John’s YouTube channel and allows him to continue to make videos like this.
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The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
The question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.
