More Spin, Less Drag
In this article, we look at how twist rate and stability affect the Ballistic Coefficient (BC) of a bullet. Again, this topic is covered in detail in the Modern Advancements book. Through our testing, we’ve learned that adequate spin-stabilization is important to achieving the best BC (and lowest drag). In other words, if you don’t spin your bullets fast enough (with sufficient twist rate), the BC of your bullets may be less than optimal. That means, in practical terms, that your bullets drop more quickly and deflect more in the wind (other factors being equal). Spin your bullets faster, and you can optimize your BC for best performance.
Any test that’s designed to study BC effects has to be carefully controlled in the sense that the variables are isolated. To this end, barrels were ordered from a single barrel smith, chambered and headspaced to the same rifle, with the only difference being the twist rate of the barrels. In this test, 3 pairs of barrels were used. In .224 caliber, 1:9” and 1:7” twist. In .243 caliber it was 1:10” and 1:8”, and in .30 caliber it was 1:12” and 1:10”. Other than the twist rates, each pair of barrels was identical in length, contour, and had similar round counts. Here is a barrel rack at the Applied Ballistics Lab:
Applied Ballistics used multiple barrels to study how twist rate affects BC.
“The Modern Advancements series is basically a journal of the ongoing R&D efforts of the Applied Ballistics Laboratory. The goal of the series is to share what we’re learning about ballistics so others can benefit.” –Bryan Litz
Barrel twist rate along with velocity, atmospherics, and bullet design all combine to result in a Gyroscopic Stability Factor (SG). It’s the SG that actually correlates to BC. The testing revealed that if you get SG above 1.5, the BC may improve slightly with faster twist (higher SG), but it’s very difficult to see. However, BC drops off very quickly for SGs below 1.5. This can be seen in the figure below from Modern Advancements in Long Range Shooting.
The chart shows that when the Gyroscopic Stability Factor (SG) is above 1.5, BC is mostly constant. But if SG falls below 1.5, BC drops off dramatically.
Note that the BC drops by about 3% for every 0.1 that SG falls below 1.5. The data supports a correlation coefficient of 0.87 for this relationship. That means the 3% per 0.1 unit of SG is an accurate trend, but isn’t necessarily exact for every scenario.
It’s a common assumption that if a shooter is seeing great groups and round holes, that he’s seeing the full potential BC of the bullets. These tests did not support that assumption. It’s quite common to shoot very tight groups and have round bullet holes while your BC is compromised by as much as 10% or more. This is probably the most practical and important take-away from this test.
To calculate the SG of your bullets in your rifle, visit the Berger Bullets online stability calculator. This FREE calculator will show you the SG of your bullets, as well as indicate if your BC will be compromised (and by how much) if the SG is below 1.5. With the stated twist rate of your barrel, if your selected bullet shows an SG of 1.5 (or less), the calculator will suggest alternate bullets that will fully stabilize in your rifle. This valuable online resource is based directly on live fire testing. You can use the SG Calculator for free on the web — you don’t need to download software.
Learn More About SG and BC This article is just a brief overview of the interrelated subjects of twist rate, Gyroscopic Stability, and BC. The coverage of twist rates in Modern Advancements in Long-Range Shooting is more detailed, with multiple live fire tests.
Other chapters in the book’s twist rate section include: · Stability and Drag – Supersonic
· Stability and Drag – Transonic
· Spin Rate Decay
· Effect of Twist rate on Precision
Other sections of the book include: Modern Rifles, Scopes, and Bullets as well as Advancements in Predictive Modeling. This book is sold through the Applied Ballistics online store. Modern Advancements in Long Range Shooting is also available in eBook format in the Amazon Kindle store.
At the 2015 Berger Southwest Nationals, Forum member Erik Cortina cornered Bryan Litz of Applied Ballistics. Erik, the F-Open winner in the 600-yard Mid-Range match, was curious about bullet sorting. Knowing that bullets can be sorted by many different criteria (e.g. weight, overall length, base to ogive length, actual bearing surface length etc.) Erik asked Bryan to specify the most important dimension to consider when sorting. Bryan recommended sorting by “Base to Ogive”. Litz noted that: “Sorting by overall length can be misleading because of the nature of the open-tip match bullet. You might get a bullet that measures longer because it has a jagged [tip], but that bullet might not fly any different. But measuring base to ogive might indicate that the bullet is formed differently — basically it’s a higher resolution measurement….”
Ballistics Q & A in Shooter’s Forum
Got more questions about bullets? Our Shooters’ Forum has a special area for Bullets & Ballistics topics. There you can get your own questions about bullets and ballistics answered by Bryan Litz and other experts from Applied Ballistics.
Competitors at the 2015 Berger Southwest Nationals were treated to something special on Saturday morning. After a short address by Eric Stecker, fireworks boomed from downrange and a flight of three warbirds streamed overhead, trailing smoke. Watch these dramatic moments in the video below.
This ceremony marked the dedication of Ben Avery’s 1000-yard range as the Middleton Tompkins Range. With his family by his side, Mid was recognized for his achievements in the shooting sports and his decades of service. This was a heart-warming event honoring Mid, a six-time National High Power Rifle Champion, and the leading member of America’s first family of shooting. Wife Nancy Tompkins and step-daughters Sherri Jo Gallagher and Michelle Gallagher have all been National rifle champions (High Power and/or Long-Range). This was an emotional day for Mid — he revealed to us that this was certainly one of the greatest highlights of his life.
Berger President Eric Stecker speaks at range dedication ceremony. Mid Tompkins stands with his family members Sherri Jo Gallagher (to Mid’s left), wife Nancy Tompkins, and Michelle Gallagher.
Along with the dedication of the 1000-yard range, a ribbon-cutting ceremony was held for the new multi-purpose facility at Ben Avery. Situated at the 1000-yard range, this facility was constructed with $420,000 in funding from Berger Bullets and Nightforce Optics. Mid Tompkins cut the red ribbon on the facility’s front doors, officially opening the multi-purpose center for public use.
Mid jokes with the crowd, showing his quick-witted sense of humor.
Panorama of Middleton Tompkins 1000-Yard Range at Ben Avery (CLICK to ZOOM)
Interview with Past NRA President John Sigler at Ben Avery
In the video below, we interview past NRA President John Sigler. An avid long-range shooter himself, John is the current chairman of the NRA High Power Committee. John was at Ben Avery this week competing in the F-Open Division. John says that the emergence of the F-Class discipline has extended his competitive shooting career. He had high praise for the Ben Avery Range and the new multi-purpose building dedicated on February 14th.
Guest Article By Michelle Gallagher, Berger Bullets
Let’s face it. In the world of firearms, there is something for everyone. Do you like to compete? Are you a hunter? Are you more of a shotgun shooter or rifle shooter? Do you enjoy running around between stages of a timed course, or does the thought of shooting one-hole groups appeal to you more? Even though many of us shoot several different firearms and disciplines, chances are very good that we all have a favorite. Are we spreading ourselves too thin by shooting different disciplines, or is it actually beneficial? I have found that participating in multiple disciplines can actually improve your performance. Every style of shooting is different; therefore, they each develop different skills that benefit each other.
How can cross-training in other disciplines help you? For example, I am most familiar with long-range prone shooting, so let’s start there. To be a successful long-range shooter, you must have a stable position, accurate ammunition, and good wind-reading skills. You can improve all of these areas through time and effort, but there are other ways to improve more efficiently. Spend some time practicing smallbore. Smallbore rifles and targets are much less forgiving when it comes to position and shot execution. Long-range targets are very large, so you can get away with accepting less than perfect shots. Shooting smallbore will make you focus more on shooting perfectly center shots every time. Another way to do this with your High Power rifle is to shoot on reduced targets at long ranges. This will also force you to accept nothing less than perfect. Shoot at an F-Class target with your iron sights. At 1000 yards, the X-Ring on a long range target is 10 inches; it is 5 inches on an F-Class target. Because of this, you will have to focus harder on sight alignment to hit a center shot. When you go back to the conventional target, you will be amazed at how large the ten ring looks.
Also, most prone rifles can be fitted with a bipod. Put a bipod and scope on your rifle, and shoot F-TR. Shooting with a scope and bipod eliminates position and eyesight factors, and will allow you to concentrate on learning how to more accurately read the wind. The smaller target will force you to be more aggressive on your wind calls. It will also help encourage you to use better loading techniques. Nothing is more frustrating than making a correct wind call on that tiny target, only to lose the point out the top or bottom due to inferior ammunition. If you put in the effort to shoot good scores on the F-Class target, you will be amazed how much easier the long-range target looks when you return to your sling and iron sights. By the same token, F-Class shooters sometimes prefer to shoot fast and chase the spotter. Shooting prone can help teach patience in choosing a wind condition to shoot in, and waiting for that condition to return if it changes.
Benchrest shooters are arguably among the most knowledgeable about reloading. If you want to learn better techniques about loading ammunition, you might want to spend some time at benchrest matches. You might not be in contention to win, but you will certainly learn a lot about reloading and gun handling. Shooting F-Open can also teach you these skills, as it is closely related to benchrest. Benchrest shooters may learn new wind-reading techniques by shooting mid- or long-range F-Class matches.
Position shooters can also improve their skills by shooting different disciplines. High Power Across-the-Course shooters benefit from shooting smallbore and air rifle. Again, these targets are very small, which will encourage competitors to be more critical of their shot placement. Hunters may benefit from shooting silhouette matches, which will give them practice when shooting standing with a scoped rifle. Tactical matches may also be good, as tactical matches involve improvising shots from various positions and distances. [Editor: Many tactical matches also involve hiking or moving from position to position — this can motivate a shooter to maintain a good level of general fitness.]
These are just a few ways that you can benefit from branching out into other shooting disciplines. Talk to the other shooters. There is a wealth of knowledge in every discipline, and the other shooters will be more than happy to share what they have learned. Try something new. You may be surprised what you get out of it. You will certainly learn new skills and improve the ones you already have. You might develop a deeper appreciation for the discipline you started off with, or you may just discover a new passion.
This article originally appeared in the Berger Bulletin. The Berger Bulletin blog contains the latest info on Berger products, along with informative articles on target shooting and hunting.
Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 2 by Bryan Litz forBerger Bullets. Part One of this series focused on the importance of COAL in terms of SAAMI standards, magazine lengths, seating depths, and pressure levels. Another measure of length for loaded ammunition is highly important to precision, namely Cartridge Base to Bullet Ogive Length (CBTO).
Figure 2. Chamber throat geometry showing the bullet jump to the rifling or lands.
Look at Figure 2. Suppose the bullet was seated out of the case to the point where the base of the bullet’s nose (ogive) just contacted the beginning of the riflings (the lands) when the bolt was closed. This bullet seating configuration is referred to as touching the lands, or touching the riflings and is a very important measurement to understand for precision hand-loading. Due to the complex dynamics of internal ballistics which happen in the blink of an eye, the distance a bullet moves out of the case before it engages the riflings is highly critical to precision potential. Therefore, in order to systematically optimize the precision of his handloads, it’s critically important that the precision hand-loader understands how to alter bullet seating depth in relation to the barrel rifling. Part of the required knowledge is understanding how to accurately and repeatably measure the Cartridge Base To Ogive (CBTO) dimension. This is explained in the FULL ARTICLE.
Bryan Litz offers an extended discussion on how to measure CBTO using different tools and methods, including the Hornady OAL gauge. You can read this discussion in the full article found on the Berger Bullets website. CLICK HERE to Read Full Article.
Why Not Use CBTO as a SAAMI Standard?
If CBTO is so important to rifle accuracy, you might ask, “Why is it not listed as the SAAMI spec standard in addition to COAL?” There is one primary reason why it is not listed in the standard. This is the lack of uniformity in bullet nose shapes and measuring devices used to determine CBTO.
Figure 4. Two different bullet shapes, seated to the same CBTO length, but different COAL. Note the shiny scratches on the bullets made by the comparator tool which indicates a point on the bullet ogive near where the ogive will engage the riflings.
Benefits of Having a Uniform CBTO
There is another aspect to knowing your CBTO when checking your COAL as it pertains to performance. With good bullets, tooling, and carefully-prepared cases you can easily achieve a CBTO that varies less than +/- .001″ but your COAL can vary as much as .025″ extreme spread (or more with other brands). This is not necessarily bad and it is much better than the other way around. If you have a CBTO dimension that varies but your COAL dimension is tight (within +/- .002″) then it is most likely that your bullet is bottoming out inside the seater cone on the bullet tip. This is very bad and is to be avoided. It is normal for bullets to have precisely the same nose shape and it is also normal for these same bullets to have nose lengths that can vary as much as .025″.
Summary of Cartridge Base To Ogive (CBTO) Discussion
Here are four important considerations regarding bullet seating depth as it relates to CBTO:
1. CBTO is a critical measurement to understand for handloaders because it’s directly related to precision potential, and you control it by simply setting bullet seating depth.
2. Tools and methods for measuring CBTO vary. Most of the measurement techniques have pitfalls (which may give rise to inconsistent results) that you should understand before starting out.
3. A CBTO that produces the best precision in your rifle may not produce the best precision in someone else’s rifle. Even if you have the same rifle, same bullets, same model of comparator gauges, etc. It’s possible that the gauges are not actually the same, and measurements from one don’t translate to the same dimension for another.
4. Once you find the CBTO that produces the best precision in your rifle, it’s important to allow minimal variation in that dimension when producing quality handloads. This is achieved by using quality bullets, tooling, and properly preparing case mouths and necks for consistent seating.
Here’s a feel-good story, particularly for those of us getting up in years. Walt Berger recently proved you are as young as you feel — and you can enjoy shooting success at any age. Walt Berger, well into his 80s, won a big benchrest victory last month, taking the Sporter Class 100-yard Aggregate at the 2014 NBRSA Score Nationals. In so doing, Walt earned his 20th Hall of Fame Point. That’s a great accomplishment for the Elder Statesman of Benchrest. Congrats to Walt! And, yes, of course, Walt was shooting a projectile made by Berger Bullets — the 6mm 65gr BT Target bullet.
About Walt Berger
Walt Berger started making rifle bullets in 1955 because he believed he could make better bullets than those that were available at the time. He regularly participated in benchrest shooting competitions (and still does today), which requires the highest levels of precision in all components. In 1987, Walt grew his bullet making operation beyond a part time hobby after encouragement from his second wife Eunice (Walt lost his first wife Mary to cancer). Together, they grew the business into a large-scale precision rifle bullet-making operation.
Walt was born at the end of the Golden Twenties and the beginning of the Great Depression. His story is about overcoming great odds and seeing things through to success when almost everyone around him was convinced he would fail.
Walt Berger with two younger generation Berger Bullets employees at the 2014 NRA Annual Meeting.
Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 1 by Bryan Litz forBerger Bullets.
Many shooters are not aware of the dramatic effects that bullet seating depth can have on the pressure and velocity generated by a rifle cartridge. Cartridge Overall Length (COAL) is also a variable that can be used to fine-tune accuracy. It’s also an important consideration for rifles that need to feed rounds through a magazine. In this article, we’ll explore the various effects of COAL, and what choices a shooter can make to maximize the effectiveness of their hand loads.
Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI)
Most loading manuals (including the Berger Manual), present loading data according to SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) standards. SAAMI provides max pressure, COAL and many other specifications for commercial cartridges so that rifle makers, ammo makers, and hand loaders can standardize their products so they all work together. As we’ll see later in this article, these SAAMI standards are in many cases outdated and can dramatically restrict the performance potential of a cartridge.
Bullet seating depth is an important variable in the accuracy equation. In many cases, the SAAMI specified COAL is shorter than what a hand loader wants to load their rounds to for accuracy purposes. In the case where a hand loader seats the bullets longer than SAAMI specified COAL, there are some internal ballistic effects that take place which are important to understand.
Effects of Seating Depth / COAL on Pressure and Velocity
The primary effect of loading a cartridge long is that it leaves more internal volume inside the cartridge. This extra internal volume has a well known effect; for a given powder charge, there will be less pressure and less velocity produced because of the extra empty space. Another way to look at this is you have to use more powder to achieve the same pressure and velocity when the bullet is seated out long. In fact, the extra powder you can add to a cartridge with the bullet seated long will allow you to achieve greater velocity at the same pressure than a cartridge with a bullet seated short.
Figure 1. When the bullet is seated farther out of the case, there is more volume available for powder. This enables the cartridge to generate higher muzzle velocity with the same pressure.
When you think about it, it makes good sense. After all, when you seat the bullet out longer and leave more internal case volume for powder, you’re effectively making the cartridge into a bigger cartridge by increasing the size of the combustion chamber. Figure 1 illustrates the extra volume that’s available for powder when the bullet is seated out long.
Before concluding that it’s a good idea to start seating your bullets longer than SAAMI spec length, there are a few things to consider.
Geometry of a Chamber Throat
The chamber in a rifle will have a certain throat length which will dictate how long a bullet can be loaded. The throat is the forward portion of the chamber that has no rifling. The portion of the bullet’s bearing surface that projects out of the case occupies the throat (see Figure 2).
The length of the throat determines how much of the bullet can stick out of the case. When a cartridge is chambered and the bullet encounters the beginning of the rifling, known as the lands, it’s met with hard resistance. This COAL marks the maximum length that a bullet can be seated. When a bullet is seated out to contact the lands, its initial forward motion during ignition is immediately resisted by an engraving force.
Seating a bullet against the lands causes pressures to be elevated noticeably higher than if the bullet were seated just a few thousandths of an inch off the lands.
A very common practice in precision reloading is to establish the COAL for a bullet that’s seated to touch the lands. This is a reference length that the hand loader works from when searching for the optimal seating depth for precision. Many times, the best seating depth is with the bullet touching or very near the lands. However, in some rifles, the best seating depth might be 0.100″ or more off the lands. This is simply a variable the hand loader uses to tune the precision of a rifle.
Accuracy 1st Development Group, a training operation based in Texas, will soon release a new instructional video: Long Range Made Easy. This training video features Bryan Litz, author of Applied Ballistics for Long Range Shooting. Many of the shooters shown in the video use the new ABM ammo developed by Bryan’s Applied Ballistics lab for Berger Bullets. Check out the preview “trailer” for Long Range Made Easy.
Watch Trailer for “Long Range Made Easy”
Accuracy 1st Scope Levels
Accuracy 1st also sells some interesting products for precision rifle shooters. Check out this unique, curved-vial scope leveler ring. More precise and sensitive than other scope levels, the Accuracy 1st leveling device can detect 1° of cant. Displayed line increments represent 2.5° of cant.
You may wonder: “Why are these scope levels better than other similar products?” Accuracy 1st explains: “Our levels are of the highest quality and accuracy. Some scope level manufacturers use plastic housings, air bubbles and sub-par glass in their vials. In lieu of a straight bubble vial, Accuracy 1st utilizes a custom curved vial featuring medical-grade glass and a ceramic ball. The use of the ceramic ball eliminates the inherent flaws associated with air bubble levels, which at higher temperatures and pressure will compromise the bubble size causing level inaccuracies. Typically air bubble levels require 3° to 5° [tilt] to even register movement. By contrast, the Accuracy 1st custom level will read movement at a minimum of 1° and will extend measurements out to +/- 10°.”
Michelle Gallagher is now the 2014 NRA Long Range High Power Rifle Champion. Michelle shot a perfect Palma score to win the multi-match championship. When the dust settled, Michelle edged out her mom, Nancy Tompkins, by a single X. Readers asked about Michelle’s choice of bullets. In the Long Range Championships, Michelle used the Berger .30-caliber 155.5gr Match Fullbore Target bullet (for Palma), as well as the 6.5mm 140gr Match Hybrid Target bullet.
Here are some photos from the Long Range championships, courtesy GONRAMedia.
John Whidden, a three-time NRA Long Range Champion, had a pair of long-range rifles built on modified Anschutz aluminum small-bore stocks. John’s scoped rig (first photo) features a Kelbly Panda Action. The iron sight version (second photo below) has a Winchester action. John has done these conversions for other shooters.
Long Range is not a man’s world by any means. The top two LR places at Perry were claimed by ladies.
Tubeguns built with Gary Eliseo chassis systems were popular on the firing line.
Yes, that is a John Deere Mirage Band shielding this shooter’s barrel.
This service rifle shooter found a way to shield his sights and remember his loved ones.
This competitor transformed a Sinclair loading block into an elevated ammo caddy. Clever piece of kit!
“Wagons HO!”. Shooters await the long ride to the pits for target duties.
Berger Bullets has improved its online stability calculator. Tests have shown that bullets can suffer from reduced BC if the bullet rpm (spin rate) is less than optimal, even if barrel twist rate is otherwise fast enough to stabilize bullets in flight. Now, the improved, free Stability Calculator can determine if you need a faster-twist barrel to enjoy the best BC from your bullets.
By Bryan Litz, Chief Ballistician forBerger Bullets
We’re happy to announce a major upgrade to our Twist Rate Stability Calculator which is free to use on the Berger Bullets webpage. The old stability calculator was pretty basic, and would simply return a gyroscopic stability number based on your bullet, twist rate, and atmospheric conditions. This was used to determine if your barrels twist rate was fast enough to stabilize a particular bullet or not, based on the Gyroscopic Stability Factor (SG) being greater than 1.4.
Stability and BC — How Bullet RPM Affects Ballistic Coefficients
The new calculator still calculates SG, but also goes much further. In addition to calculating stability, the upgraded calculator can also tell you if your stability level is harming the effective BC of your bullets or not. Extensive testing has proven that bullets fired with stability levels between 1.2 and 1.5 can fly with excellent precision (good groups), but suffer from a depressed BC, sometimes as much as 10%. Shooting the bullets from faster twist rate barrels allows for the bullets to fly better and realize their full BC potential.
Last month, in the Daily Bulletin, we talked about twist rate and muzzle velocity. That discussion was based on a detailed study published in Modern Advancements in Long Range Shooting.
This article is just a brief overview of the interrelated subjects of twist rate, Gyroscopic Stability, and BC. The coverage of twist rates in Modern Advancements in Long-Range Shooting is more detailed, with multiple live fire tests.
Position shooters can also improve their skills by shooting different disciplines. High Power Across-the-Course shooters benefit from shooting smallbore and air rifle. Again, these targets are very small, which will encourage competitors to be more critical of their shot placement. Hunters may benefit from shooting silhouette matches, which will give them practice when shooting standing with a scoped rifle. Tactical matches may also be good, as tactical matches involve improvising shots from various positions and distances. [Editor: Many tactical matches also involve hiking or moving from position to position — this can motivate a shooter to maintain a good level of general fitness.]
Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 2
