May 9th, 2018

Elements of Long Range Shooting Video Series

Bryan Litz Elements Long Range Shooting NSSF Ballistics Coeffecient Atmospherics

Want to learn more about Long Range Shooting? Check out the “Elements of Long Range Shooting” videos from the National Shooting Sport Foundation (NSSF). In this multi-part series, Bryan Litz of Applied Ballistics covers a variety of topics of interest to precision shooters. Today we feature three of these videos. There are five other videos in this series. Watch the entire 8-video “Elements of Long Range Shooting” series on the NSSF YouTube Channel.

Litz NSSF Video Elements long range shooting Raton NM ELR

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 air density 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.

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.”

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 recently received a major U.S. defense contract to to execute Phase 1 of the Extreme Sniper Strike Operations (ESSO) project.

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November 15th, 2016

Altitude, Air Pressure and Ballistics — What You Need to Know

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.

Suunto AltimeterOne 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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August 6th, 2016

How to Work with Density Altitude in Ballistics Calculations

In this video, Bryan Litz of Applied Ballistics talks about Density Altitude and the effect of atmospheric conditions on bullet flight. Bryan explains why you must accurately account for Density Altitude when figuring long-range trajectories.

Bryan tells us: “One of the important elements in calculating a fire solution for long-range shooting is understanding the effect of atmospherics. Temperature, pressure, and humidity all affect the air density that the bullet’s flying through. You can combine all those effects into one number (value) called ‘Density Altitude’. That means that you just have one number to track instead of three. But, ultimately, what you are doing is that you are describing to your ballistics solver the characteristics of the atmosphere that your bullet’s flying through so that the software can make the necessary adjustments and account for it in its calculations for drop and wind drift.”

Bryan adds: “Once you get past 500 or 600 yards you really need to start paying careful attention to atmospherics and account for them in your ballistic solutions”. You can learn more about Density Altitude in Bryan’s book, Applied Ballistics for Long Range Shooting (Third Edition).

General Scientific Definition of Density Altitude

Density altitude is the altitude relative to the standard atmosphere conditions (ISA) at which the air density would be equal to the indicated air density at the place of observation. Density altitude can be calculated from atmospheric pressure and temperature (assuming dry air). Here is the formula:

Litz Ballistics Density Altitude

Air is more dense at lower elevations primarily because of gravity: “As gravity pulls the air towards the ground, [lower] molecules are subject to the additional weight of all the molecules above. This additional weight means the air pressure is highest at sea level, and diminishes with increases in elevation”.*

Both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.

*Source: Miningandconstruction.com

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October 19th, 2014

How Altitude and Air Pressure Influence Ballistics

Suunto AltimeterOne 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 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 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.

Trajectory of Bullet fired at Sea Level

Trajectory of Bullet fired at 20,000 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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May 14th, 2011

GEAR REVIEW: Field Density Altitude Compensator

by Ian Kenney
A week before the fall Allegheny Sniper Challenge (ASC), I first saw Adaptive’s Field Density Altitude Compensator (FDAC). I was impressed by its capabilities and compact size and I managed to take one home from the ASC prize table the very next weekend. The FDAC comes from Adaptive Consulting and Training Services in Stafford, VA. The guys at Adaptive know a thing or two about long-range shooting — many of them are former USMC Scout Snipers. Their long-range shooting and combat experience helped them perfect the FDAC.

At first glance the $39.95 FDAC appears to be just another data card. However, in a number of ways, it is completely different than traditional data cards. The FDAC was designed to be simple and accurate, so that any military or civilian shooter could pick it up and, within minutes, effectively employ it. Anyone familiar with a Midot Master should find the FDAC simple and intuitive. Another plus is that, unlike electronic gadgets, the FDAC doesn’t need batteries or shielding from the elements. You don’t have to carry around extra batteries, chargers, and “ruggedized” weather-proof cases.

FDAC Offers Multiple Cards for More Precise Solutions
The FDAC is quite different than traditional data cards that calculate trajectories based on a single muzzle velocity in a given set of conditions. The problem with those traditional data cards is that, as soon as one variable changes, the card’s ballistic solution becomes less valid. The FDAC solves this problem by employing several cards for different muzzle velocities and using Density Dltitude to compensate for the differences in environmental conditions. For the uninitiated, Density Altitude combines the temperature, humidity, barometric pressure, and elevation figures into one number that is more easily used over a wider range of conditions. Density Altitude can be obtained with a portable weather station (such as a Kestrel). If a portable weather meter is not available, the basic chart printed on the card itself works pretty well even when guessing at the physical altitude and temperature.

Adaptive FDAC ranging card
CLICK HERE for FDAC Users’ Guide PDF

FDAC Ballistic Solutions Deliver First-Round Hits in the Field
I first tested the FDAC at Reade Range in Pennsylvania, shooting from 500 to 1000 yards. I used the 2700 fps velocity card that came with my FDAC for the 175 Sierra Match King since that most closely matched what I had loaded up. Starting out with a cold bore shot from the 500-yard line, I obtained the density altitude using my Brunton ADC Pro, and slid the card over until the proper density altitude column was showing. With 3.2 mils of elevation and .2 mils of left wind dialed into my Nightforce 3.5-15×50 (first focal plane) scope, I went for my cold bore shot, hoping the FDAC would put me close. I was happily rewarded with a first round, center mass hit, just a little left of center.

The FDAC continued to shine at longer ranges. FDAC solutions gave me first-round hits at 600 and 800 yards, a second round hit at 1000 yards. Several weeks later I found myself in a field in rural North Carolina once again putting the FDAC to good use this time without any electronic aids. To my surprise, my guestimate of about 500’ for density altitude was pretty darn close to what the Kestrel my friend had was saying also. Just like at Reade Range, the FDAC values delivered cold bore hits that were nearly point of aim = point of impact. That demonstrated how well the FDAC worked in warm weather.

This winter I was able to see how the FDAC performed in cold conditions. In cooler, denser air, a bullet requires more elevation correction to get on target than it would need in warmer temps. So I went out one chilly January morning and confirmed that the FDAC can handle cold conditions. The FDAC solutions once again gave me first round hits from 250 yards to 730 yards. The little DA chart put me in the right vicinity for density altitude just by knowing my altitude and making a guess for the air temperature. Since I’ve started using the FDAC I’ve found that the data is either spot on or within about .2 mils of the correct dope at nearly all distances when using the correct density altitude column. This is very impressive. I found that the FDAC delivered practically the same data as popular digital PDAs and field ballistic calculators. But the FDAC can be even faster in use (once you become familiar with its operation), and, at $39.95, it costs a fraction of what a dedicated electronic ballistics solver would cost. The FDAC is practical, very accurate, inexpensive, compact, lightweight and never needs batteries — what’s not to like?

Below is a SnipersHide Video Review of the FDAC Tool

New Enhanced Milspec FDAC Released this Year
Adaptive has put much R&D into the FDAC and it shows. Thousands of Field Density Altitude Compensators have been provided to soldiers and marines, who are making good use of the devices. At the 2011 SHOT Show, Adaptive unveiled an enhanced FDAC, the MILSPEC-XR. This new version includes a new Density Altitude calculator, extended range dope for the .338LM and .300WM, as well as tools for slope dope and moving targets. Adaptive also offers conversion tables and compatibility charts so that the FDAC can be used with other bullets besides the original FDAC default projectiles. (For FDAC owners, the conversion charts are FREE!) The FDAC is truly one of those few products that I wish I had when I was deployed to Afghanistan. I highly recommend it to any long-range shooter using .308 Win, .300WM or .338LM cartridges (with a mil-based optic). For more information, or to order an FDAC tool, visit the Adaptive website, ACTSVirginia.com, or call (540) 657-8541.

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