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August 16th, 2024
Photo shows the new ZEISS LRP S5 318-50 first focal plane (FFP) scope.
“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:
Section 3.0: Exterior Ballistic Effects on Bullet Flight
Section 3.1: Effects of Altitude and Atmospheric Conditions
Section 3.2: Effects of Wind
Section 3.3: Effects of Shooting Uphill or Downhill
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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September 28th, 2023
Photo shows the new ZEISS LRP S5 318-50 first focal plane (FFP) scope.
“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:
Section 3.0: Exterior Ballistic Effects on Bullet Flight
Section 3.1: Effects of Altitude and Atmospheric Conditions
Section 3.2: Effects of Wind
Section 3.3: Effects of Shooting Uphill or Downhill
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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November 21st, 2022
Photo shows the new ZEISS LRP S5 318-50 first focal plane (FFP) scope.
“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:
Section 3.0: Exterior Ballistic Effects on Bullet Flight
Section 3.1: Effects of Altitude and Atmospheric Conditions
Section 3.2: Effects of Wind
Section 3.3: Effects of Shooting Uphill or Downhill
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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October 19th, 2021
Photo shows the new ZEISS LRP S5 318-50 first focal plane (FFP) scope.
“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:
Section 3.0: Exterior Ballistic Effects on Bullet Flight
Section 3.1: Effects of Altitude and Atmospheric Conditions
Section 3.2: Effects of Wind
Section 3.3: Effects of Shooting Uphill or Downhill
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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August 1st, 2019
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.
One of our readers asked “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, 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′ ASL or less. I’ll need about 29-30 MOA to get from 100 yard to 1000 yards with a Berger 155gr VLD @ 2960fps. By contrast, in Raton, NM, located at 6600′ ASL, 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.”
If you want to learn more about all aspects of External Ballistics, ExteriorBallistics.com provides a variety of useful resources. In particular, on that site, Section 3.1 of the Sierra Manual is reprinted, covering Effects of Altitude and Atmospheric Pressure on bullet flight.
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November 15th, 2016
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.
One of our readers asked “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, 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′ ASL or less. I’ll need about 29-30 MOA to get from 100 yard to 1000 yards with a Berger 155gr VLD @ 2960fps. By contrast, in Raton, NM, located at 6600′ ASL, 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.”
If you want to learn more about all aspects of External Ballistics, ExteriorBallistics.com provides a variety of useful resources. In particular, on that site, Section 3.1 of the Sierra Manual is reprinted, covering Effects of Altitude and Atmospheric Pressure on bullet flight.
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February 20th, 2011
 There’s a lot of buzz about ballistics programs for smartphones. Those are handy, to be sure, but most people still need a solid, full-featured program to run on their home computers. Berger Bullets offers a sophisticated ballistics programs for MS Windows computers that works really well, and lets you print out results. Up-to-Date G7 BCs for Berger projectiles are built-in to the program, and the price is right — FREE.
CLICK HERE to Download Berger Ballistics Program
The program is basic enough to be easy to use, but flexible enough to allow you to calculate custom ballistics for your rifle and load. The program accounts for all the basic external ballistic parameters including bullet BC and muzzle velocity, atmospherics, uphill/downhill shooting, etc. The output tabulates velocity, energy and time of flight as a function of range. Bullet path and wind deflection are displayed in your choice of inches, centimeters, MOA or MILS.
 Instructions for Program
On the Berger Bullets Blog (1/26/2010), You’ll find a description of program features and a complete set of instructions. Here are instructions for the bullet variables: “The bullet inputs are straightforward. The BC can be entered in reference to either the G1 or G7 standard. You can find the G1 or G7 BC for your bullet either printed on the bullet box label, or on our products page. For accurate results, you should measure the muzzle velocity with a good chronograph. If you don’t have access to a chronograph, you can estimate the muzzle velocity based on your load data.”
Tips for Best Results
Bryan Litz includes tips on getting the most from the Berger Ballistics program. Some of Bryan’s suggestions will also help you when working with other ballistics software:
G1 vs. G7 BC: The accuracy of the ballistic solution is only as accurate as the inputs you give it. The advertised BCs for Berger bullets are established by actual field firing tests over long range and are very accurate. Using the properly referenced BC (G7 vs. G1) for the bullet you’re modeling is important. For any bullet with a boat tail, we recommend using the G7 BC.
Muzzle Velocity: Knowing your true muzzle velocity is important when calculating external ballistics. It’s best to measure your muzzle velocity directly with a chronograph.
Altitude and Atmosphere: If you want a truly accurate long-range trajectory prediction, you can’t ignore atmospheric effects. This is especially true the farther you get from standard conditions (sea level altitude, 59 degrees Fahrenheit, 0% humidity).
Scope Verification: It’s important to verify the most important link between the calculated ballistics and your point of impact: your scope. If the ballistics program calculates 30.0 MOA of drop for a particular shot, and you dial your scope to 30.0 MOA, are you sure it’s giving you exactly 30.0 MOA? In reality, many scopes have enough error in them to cause misses at long range. It’s important to verify the value of your scope clicks by firing groups at short range.
If you have further questions not answered on Berger’s Blog Page, email Bryan.Litz [at] bergerbullets.com. NOTE: If your computer won’t run the program, please download and install this Java update: http://www.java.com/en/download/index.jsp. This is a Windows PC program. You may have problems trying to run it on a MAC in emulation.
Story sourced by Edlongrange.
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November 27th, 2009
One of our readers asked “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, the bullet behaves as if it has a higher ballistic coefficient.
Forum members Milanuk explain 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′ ASL or less. I’ll need about 29-30 MOA to get from 100 yard to 1000 yards with a Berger 155gr VLD @ 2960fps. By contrast, in Raton, NM, located at 6600′ ASL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
One thing to remember — 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.
One important thing to remember is 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 Kestral, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.”
You can do your own experimental calculations using the JBM Online Ballistics Program (free to use). Here are two printouts, 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.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
Here’s a useful resource on External Ballistics if you want to learn more about the effects of altitude and barometric pressure on bullet flight.
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