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January 4th, 2024

Long Range Shooting on a Spinning Planet — The Coriolis Effect

Whittington Coriolis Effect
Photo by Dustin Ellermann at Whittington Center Range.

The Coriolis Effect comes into play with extreme long-range shots like this (2100 yards at Raton, New Mexico). The rotation of the earth actually moves the target a small distance (in space) during the long duration of the bullet’s flight.

Coriolis Effect Bryan Litz Applied BallisticsWhen you’re out at the range, the Earth seems very stable. But it is actually a big sphere zooming through space while spinning around its axis, one complete turn every 24 hours. The rotation of the earth can create problems for extreme long-range shooters. During extended bullet flight times, the rotation of the planet causes an apparent deflection of the bullet path over very long distances. This is the ballistics manifestation of the Coriolis Effect.

Bryan Litz of Applied Ballistics discusses explains the Coriolis Effect in his Ballistics Books and Seminars. Bryan notes that Coriolis is “a very subtle effect. People like to make more of it than it is because it seems mysterious.” In most common shooting situations inside 1K, Coriolis is not important. 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.

Bryan explains: “The Coriolis Effect… has to do with the spin of the earth. You are basically shooting from one point to another on a rotating sphere, in an inertial reference frame. 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.”

Coriolis Effect Bryan Litz Applied Ballistics

Coriolis is a very subtle effect. With typical bullet BCs and velocities, you must get to at least 1000 yards before Coriolis amounts to even one click. Accordingly, Bryan advises: “Coriolis Effect is NOT something to think about on moving targets, it is NOT something to think about in high, uncertain wind environments because there are variables that are dominating your uncertainty picture, and the Coriolis will distract you more than the correction is worth.”

“Where you could think about Coriolis, and have it be a major impact on your hit percentage, is if you are shooting at extended range, at relatively small targets, in low-wind conditions. Where you know your muzzle velocity and BC very well, [and there are] pristine conditions, that’s where you’re going to see Coriolis creep in. You’ll receive more refinement and accuracy in your ballistics solutions if you account for Coriolis on those types of shots. But in most practical long-range shooting situations, Coriolis is NOT important. What IS important is to understand is when you should think about it and when you shouldn’t, i.e. when applying it will matter and when it won’t.”

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December 16th, 2023

Long Range Experts Podcast — Bryan Litz and Emil Praslick

Long Range Grad School Podcast Guns magazine Bryan Litz Emil Praslick III Wind coaching ballistics

Applied Ballistics Founder Bryan Litz and Former USAMU and Team USA coach Emil Praslick III share their wisdom in an informative Guns Magazine Podcast. Along with being a true ballistics guru, Bryan Litz is an outstanding competitive shooter, having won F-TR National Championships, and both Sling and F-TR divisions at the Berger SW Nationals, along with many other matches. Emil is considered one of the world’s great wind-readers and team coaches, having coached 20+ championship teams.

Guns Magazine podcast host Brent Wheat asks Bryan and Emil about multiple topics including: exterior ballistics, bullet design, wind reading, ballistic solvers, BC myths, and more.

Brent reports: “Together, Bryan and Emil understand what happens from the time a bullet leaves the muzzle until it impacts the target, including the atmospheric affects along the way. Grab a pencil, listen in, and get ready to take notes.”

This Long Range Grad School podcast features Berger’s Chief Ballistician, Bryan Litz, and Berger’s Emil Praslick. Both have extensive long range competitive shooting experience, with championship titles (as shooter and/or coach) in a multitude of long range disciplines. CLICK arrow below to start podcast audio:

Long Range Grad School Podcast Guns magazine Bryan Litz Emil Praslick III Wind coaching ballistics

Emil Praslick (left) confers with Bryan Litz (right) at King of 2 Miles ELR Event.
Bryan Litz KO2M ELR podcast wind reading

In this Video Emil Praslick explains his methods for determining wind direction.

Bryan Litz coaching Team USA in Canada using a WIND PLOT.

Permalink Competition, Shooting Skills, Tech Tip 1 Comment »
November 30th, 2023

The Right Way to Find Wind Direction with a Kestrel Wind Meter

Kestrel Wind Meter Direction Vane Applied Ballistics

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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October 6th, 2023

Bullet Flight Video Shows Shock Wave + Bullet Base Drag

Science Accuracy Academy bullet video Schlieren movie shock wave capture

Ever wondered what the air around a moving supersonic bullet really looks like? Check out this video from the Bryan Litz Ballistics Facebook page. This is a Schlieren video* of a 6mm 109gr Berger LRHT bullet at about 2800 fps as fired from Francis Colon’s PRS rifle at the Applied Ballistics Lab.


Bryan Litz notes: “You can clearly see the compression (shock) wave at the front of the bullet. A compression wave is formed when the air has to move faster than the speed of sound to get out of the way, which is certainly the case for this bullet which is moving about 2.5 times the speed of sound (Mach 2.5).

That shock wave is the ‘snap’ you hear when bullets fly past you if/when you’re downrange. Also, compressing the air into a shockwave takes energy, and that energy comes directly out of the forward velocity of your bullet and gets converted into heat and noise as the shock wave forms and dissipates.

The turbulent wake at the base of the bullet shows where/how base drag applies. The third and smallest component of drag for a supersonic bullet is skin friction drag, which is a viscous boundary layer effect, and is the least visible in this image. So as you head to the range or the hunting stand, think about the absolute violence your bullets are committing in the atmosphere, before they even reach the target!”

Subscribe to the Science of Accuracy Academy for more precision rifle and long range shooting content. LINK: TheScienceofAccuracy.com.


* Schlieren imaging makes air flow features visible. SEE Schlieren Photography Wikipedia page.

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September 28th, 2023

How Altitude Affects Ballistics — Hunters Take Note

altitude ballistics zeiss LRP S5 318-50 FFP scope
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.

Suunto AltimeterThe 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 19th, 2023

“How Do Bullets Fly” — Great Online Resource with Smart Science

Bullet External Ballistics
“The overturning moment MW tends to rotate the bullet about an axis, which goes through the CG (center of gravity) and which is perpendicular to the plane of drag….

Ruprecht Nennstiel, a forensic ballistics expert from Wiesbaden, Germany, has authored a great resource about bullet behavior in flight. Nennstiel’s comprehensive article, How Do Bullets Fly, explains all the forces which affect bullet flight including gravity, wind, gyroscopic effects, aerodynamic drag, and lift. Nennstiel even explains the rather arcane Magnus Force and Coriolis Effect which come into play at long ranges. Nennstiel’s remarkable resource contains many useful illustrations plus new experimental observations of bullets fired from small arms, both at short and at long ranges.

Shadowgraph of .308 Winchester Bullet

Bullet External Ballistics

A convenient index is provided so you can study each particular force in sequence. Writing with clear, precise prose, Nennstiel explains each key factor that affects external ballistics. For starters, we all know that bullets spin when launched from a rifled barrel. But Nennstiel explains in greater detail how this spinning creates gyroscopic stability:

“The overturning moment MW tends to rotate the bullet about an axis, which goes through the CG (center of gravity) and which is perpendicular to the plane of drag, the plane, formed by the velocity vector ‘v’ and the longitudinal axis of the bullet. In the absence of spin, the yaw angle ‘δ’ would grow and the bullet would tumble.

If the bullet has sufficient spin, saying if it rotates fast enough about its axis of form, the gyroscopic effect takes place: the bullet’s longitudinal axis moves into the direction of the overturning moment, perpendicular to the plane of drag. This axis shift however alters the plane of drag, which then rotates about the velocity vector. This movement is called precession or slow mode oscillation.”

Raise Your Ballistic IQ
Though comprehensible to the average reader with some grounding in basic physics, Nennstiel’s work is really the equivalent of a Ph.D thesis in external ballistics. You could easily spend hours reading (and re-reading) all the primary material as well as the detailed FAQ section. But we think it’s worth plowing into How Do Bullets Fly from start to finish. We suggest you bookmark the page for future reference. You can also download the complete article for future reference and offline reading.

CLICK HERE for “How Do Bullets Fly” complete text.

(1.2 MB .zip file)

Photo and diagram © 2005-2009 Ruprecht Nennstiel, All Rights Reserved.

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August 8th, 2023

Ammo Encyclopedia 7th Ed. — Over 300 Cartridge Illustrations

Brussard ammunition encyclopedia 7th Edition

Wouldn’t it be nice to have a print resource that has hundreds of true-size cartridge illustrations, plus technical descriptions of thousands of popular cartridge types? That could be a real time-saver. It’s no wonder this Ammo Encyclopedia book is an Amazon category best-seller.

If you’re a serious shooter, the latest 7th Edition of the Ammo Encyclopedia belongs in your library. This 928-page book by Charles Priore Jr. and Lisa Buening is probably the most comprehensive and up-to-date book in print covering current and classic cartridges and shotshells. The Ammo Encyclopedia is a massive resource work. The 7th Edition, released in October 2022, now boasts 100+ chapters, covering thousands of handgun, rifle, and shotgun cartridges. This 928-page softcover book sells for $44.42 on Amazon.

One of the best features is a full-color section depicting actual size drawings of over 300 current rimfire/centerfire cartridges and shotshells. You won’t find that many “life-size” cartridge drawings in one place even on the internet. Cartridge profiles and ballistic charts have been expanded to include many new factory cartridges. An expanded Trademark Index lists contact information for all current ammunition manufacturers.

For the 7th Edition, over 150 cartridge types have been added. And dozens of previously proprietary cartridges now have individual profiles. An expanded color section shows current centerfire, rimfire, and shotshell cartridges in full color. Plus updated Ballistic Tables provide muzzle velocity, dimensions, and page numbers for the corresponding cartridge profile pages.

Brussard ammunition encyclopedia 5th Edition

Comments from guys who bought the book:

“[The Ammo Encyclopedia is] better than Cartridges of the World. Much better editing and more accurate.” — John Guibert

“The amount and depth of detail provided is beyond impressive. An enormous amount of time and thought went into this latest version of the Ammo Encyclopedia.” — BW Kreisler

“I have many books on firearms and ammunition acculmulated over a few decades. This is by far the best and most comprehensive book on ammunition that I have ever seen. It is a must have reference source for everthing ammunition whether for current or obsolete and the history behind them.” – Eric

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August 4th, 2023

Test Your Ballistics Smarts with Shoot 101 Quiz

Shoot 101 Quiz
How much of an expert are you when it comes to firearms and ballistics? Test your knowledge with this interactive test. Guns & Ammo magazine created a series of features called Shoot 101. These articles provide “how to” information about shooting, optics, and outdoor gear.

On the Guns & Ammo website, you’ll find the Shoot 101 Ballistics Quiz. The 15 questions are pretty basic, but it’s still fun to see if you get all the answers correct.

You don’t need a lot of technical knowledge. And it’s not all about flight ballistics. Roughly a third of the questions are about projectile types and bullet construction. Note, for some reason the layout doesn’t show all the possible answers at first. So, for each question, be sure to scroll down using the blue scroll bar on the right.

CLICK HERE to Go to Ballistics QUIZ Page »


Sample Ballistics Question

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July 23rd, 2023

Ammo Encyclopedia 7th Edition — Great Resource for Shooters

Brussard ammunition encyclopedia 7th Edition

Wouldn’t it be nice to have a print resource at your fingertips that has hundreds of true-size cartridge illustrations, plus technical descriptions of thousands of popular cartridge types? That could be a real time-saver. It’s no wonder this book is an Amazon category best-seller.

If you’re a serious shooter, the latest 7th Edition of the Ammo Encyclopedia belongs in your library. Released in late 2022, this 928-page book is probably the most comprehensive and up-to-date book in print covering current and obsolete cartridge and shotshell types. The Ammo Encyclopedia is a massive resource work with 100+ chapters, covering thousands of handgun, rifle, and shotgun cartridges from the past century and a half. This 928-page edition includes over 150 new cartridge profiles. An expanded Trademark Index lists contact information for all current ammunition manufacturers.

One of the best features is a full-color section with actual size drawings of over 320 current rimfire/centerfire cartridges and shotshells. You won’t find that many “life-size” cartridge drawings in one place even on the internet. Cartridge profiles and ballistic charts have been expanded to include many new factory cartridges. An updated Cartridge Index lists both the standard and alternate names for each cartridge in chronological order. The authors have even included air rifle pellets and historical images and charts. This 928-page softcover book is now $44.93 on Amazon.

Brussard ammunition encyclopedia 5th Edition

Comments from guys who bought the book:

“This book contains a vast array of information on many modern and even obsolete ammunition. Definitely recommend for any modern reloader novice or experienced.” – Duggaboy460

“It’s a great reference book for individuals who reload their own ammunition. There is a lot more info in this Edition. Everyone who likes this information should have it in their library.” – Reloader

“I like the general and technical comments that are available for each and every cartridge. Information that predicts if a cartridge will stay in production for many more years or rapidly become obsolete.” – RSL1

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July 13th, 2023

G1 vs. G7 Ballistic Coefficient Models — What You Need to Know

G1 G7 BC drag models

Over the past 12 months, this article was one of the TOP TEN most-read Daily Bulletin features. We’re reprising it today for those who may have missed it the first time. The above diagram comes from a TiborasurasRex YouTube Video comparing G1 and G7 BC models. CLICK HERE to watch the video.

G1 G7 BC drag modelsThe better, up-to-date ballistics programs let you select either G1 or G7 Ballistic Coefficient (BC) values when calculating a trajectory. The ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight. You’ve probably seen that G7 values are numerically lower than G1 values for the same bullet (typically). But that doesn’t mean you should select a G1 value simply because it is higher.

Some readers are not quite sure about the difference between G1 and G7 models. One forum member wrote us: “I went on the JBM Ballistics website to use the web-based Trajectory Calculator and when I got to the part that gives you a choice to choose between G1 and G7 BC, I was stumped. What determines how, or which one to use?”

The simple answer is the G1 value normally works better for shorter flat-based bullets, while the G7 value should work better for longer, boat-tailed bullets.

G1 vs. G7 Ballistic Coefficients — Which Is Right for You?
G1 and G7 refer both refer to aerodynamic drag models based on particular “standard projectile” shapes. The G1 shape looks like a flat-based bullet. The G7 shape is quite different, and better approximates the geometry of a modern long-range bullet. So, when choosing your drag model, G1 is preferable for flat-based bullets, while G7 is ordinarily a “better fit” for longer, boat-tailed bullets.

G1 G7 Ballistic coefficients

Drag Models — G7 is better than G1 for Long-Range Bullets
Many ballistics programs still offer only the default G1 drag model. Bryan Litz, author of Applied Ballistics for Long Range Shooting, believes the G7 standard is preferable for long-range, low-drag bullets: “Part of the reason there is so much ‘slop’ in advertised BCs is because they’re referenced to the G1 standard which is very speed sensitive. The G7 standard is more appropriate for long range bullets. Here’s the results of my testing on two low-drag, long-range boat-tail bullets, so you can see how the G1 and G7 Ballistic coefficients compare:

G1 BCs, averaged between 1500 fps and 3000 fps:
Berger 180 VLD: 0.659 lb/in²
JLK 180: 0.645 lb/in²

The reason the BC for the JLK is less is mostly because the meplat was significantly larger on the particular lot that I tested (0.075″ vs 0.059″; see attached drawings).

For bullets like these, it’s much better to use the G7 standard. The following BCs are referenced to the G7 standard, and are constant for all speeds.

G7 BCs:
Berger 180 VLD: 0.337 lb/in²
JLK 180: 0.330 lb/in²

Many modern ballistics programs, including the free online JBM Ballistics Program, are able to use BCs referenced to G7 standards. When available, these BCs are more appropriate for long range bullets, according to Bryan.

[Editor’s NOTE: BCs are normally reported simply as an 0.XXX number. The lb/in² tag applies to all BCs, but is commonly left off for simplicity.]

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May 15th, 2023

How to Make Your Own Laminated Cards with Ballistics Data

laminated ballistics Card print-out

Tactical competitor Zak Smith stores his elevation and wind drift data on a handy laminated data card. To make one, first generate a come-up table, using one of the free online ballistics programs such as JBM Ballistics. You can also put the info in an Excel spreadsheet or MS Word table and print it out.

Above is a sample of a data card. For each distance, the card includes drop in inches, drop in MOA, drop in Mils. It also shows drift for a 10-mph cross wind, expressed in inches, MOA, and mils. Zak explained that “to save space… I printed data every 50 yards. For an actual data-card, I recommend printing data every 20 or 25 yards.” But Zak also advised that you’ll want to customize the card format to keep things simple: “The sample card has multiple sets of data to be more universal. But if you make your own data card, you can reduce the chance of a mistake by keeping it simple.”

Once you have the card you can fold it in half and then have it laminated at a local office store or Kinko’s. Keep this in your pocket, tape it to your stock, or tie the laminated card to your rifle. If you regularly shoot at both low and high elevations, you may want to create multiple cards (since your ballistics change with altitude). To learn more about ballistic tables and data cards, check out the excellent “Practical Long-Range Rifle Shooting–Part 1″ article on Zak’s website.

ballistics data scope coverScope-Cover Mounted Ballistics Table
Another option is to place your ballistics card on the back of the front flip-up scope cover. This set-up is used by Forum member Greg C. (aka “Rem40X”).

With your ‘come-up’ table on the flip-up cover you can check your windage and elevation drops easily without having to move out of shooting position.

Greg tells us: “Placing my trajectory table on the front scope cover has worked well for me for a couple of years and thought I’d share. It’s in plain view and not under my armpit. And the table is far enough away that my aging eyes can read it easily. To apply, just use clear tape on the front objective cover.”

Links for JBM Ballistics Program

JBM Calculations Entry: JBMballistics.com/ballistics/calculators/calculators.shtml

JBM Advanced Trajectory Calculator: JBMballistics.com/cgi-bin/jbmtraj-5.1.cgi

JBM Simple Trajectory Calculator: JBMballistics.com/cgi-bin/jbmtraj_simp-5.1.cgi

JBM Trajectory Cards (Come-up Table): JBMballistics.com/cgi-bin/jbmcard-5.1.cgi

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February 5th, 2023

G1 vs. G7 Ballistic Coefficients — What You Need to Know

G1 G7 BC drag models

Over the past 12 months, this article was one of the TOP 20 most-read Daily Bulletin features. We’re reprising it today for those who may have missed it the first time. The above diagram comes from a TiborasurasRex YouTube Video comparing G1 and G7 BC models. CLICK HERE to watch the video.

The better, up-to-date ballistics programs let you select either G1 or G7 Ballistic Coefficient (BC) values when calculating a trajectory. The ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight. You’ve probably seen that G7 values are numerically lower than G1 values for the same bullet (typically). But that doesn’t mean you should select a G1 value simply because it is higher.

Some readers are not quite sure about the difference between G1 and G7 models. One forum member wrote us: “I went on the JBM Ballistics website to use the web-based Trajectory Calculator and when I got to the part that gives you a choice to choose between G1 and G7 BC, I was stumped. What determines how, or which one to use?”

The simple answer is the G1 value normally works better for shorter flat-based bullets, while the G7 value should work better for longer, boat-tailed bullets.

G1 vs. G7 Ballistic Coefficients — Which Is Right for You?
G1 and G7 refer both refer to aerodynamic drag models based on particular “standard projectile” shapes. The G1 shape looks like a flat-based bullet. The G7 shape is quite different, and better approximates the geometry of a modern long-range bullet. So, when choosing your drag model, G1 is preferable for flat-based bullets, while G7 is ordinarily a “better fit” for longer, boat-tailed bullets.

G1 G7 Ballistic coefficients

Drag Models — G7 is better than G1 for Long-Range Bullets
Many ballistics programs still offer only the default G1 drag model. Bryan Litz, author of Applied Ballistics for Long Range Shooting, believes the G7 standard is preferrable for long-range, low-drag bullets: “Part of the reason there is so much ‘slop’ in advertised BCs is because they’re referenced to the G1 standard which is very speed sensitive. The G7 standard is more appropriate for long range bullets. Here’s the results of my testing on two low-drag, long-range boat-tail bullets, so you can see how the G1 and G7 Ballistic coefficients compare:

G1 BCs, averaged between 1500 fps and 3000 fps:
Berger 180 VLD: 0.659 lb/in²
JLK 180: 0.645 lb/in²

The reason the BC for the JLK is less is mostly because the meplat was significantly larger on the particular lot that I tested (0.075″ vs 0.059″; see attached drawings).

For bullets like these, it’s much better to use the G7 standard. The following BCs are referenced to the G7 standard, and are constant for all speeds.

G7 BCs:
Berger 180 VLD: 0.337 lb/in²
JLK 180: 0.330 lb/in²

Many modern ballistics programs, including the free online JBM Ballistics Program, are able to use BCs referenced to G7 standards. When available, these BCs are more appropriate for long range bullets, according to Bryan.

[Editor’s NOTE: BCs are normally reported simply as an 0.XXX number. The lb/in² tag applies to all BCs, but is commonly left off for simplicity.]
This article is copyright 2023 AccurateShooter.com. No 3rd Party republication of this article is allowed without advance approval and payment of licensing fees.

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