You may not realize it… but to get the optimum BC from your bullets (i.e. the lowest aerodynamic drag), you must spin the bullets fast enough. Bullet drag increases (as expressed by lower BC) if the bullet spins too slowly. Bryan Litz of Applied Ballistics explains how BC changes with twist rates…
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.
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.”
“Garbage In, Garbage Out.” You have to input key variables with precision if you want your Ballistics Apps to deliver reliable long-range trajectories. So says Tom Beckstrand, Field Editor for Guns & Ammo magazine. A former U.S. Army Special Forces Officer, and avid long-range competitor, Beckstrand knows the importance of using your ballistic calculator correctly. Here are his tips on how to achieve the best results using Ballistics Calculators.
“The most important inputs to make any ballistic calculator work correctly are muzzle velocity, ballistic coefficient, and sight height,” says Beckstrand.
Ascertain Accurate Muzzle Velocity with a Good Chronograph
“Cheap chronographs will not give an accurate muzzle velocity, so the serious shooter needs to spend the money on a quality chrono.” When you chronograph, make sure to measure the distance from the muzzle to the chrono unit. That input is also important to your Ballistic calculations.
Use Reliable G1 and G7 Ballistic Coefficients
Beckstrand added, “Ballistic Coefficients are available from ammunition and bullet manufacturers, and most of these coefficients the manufacturers provide are really quite accurate.” Ballistic Coefficient or BC, is a number that reflects how well a bullet cuts through the air. The higher the BC, the less the bullet is affected by air drag.
Measure Sight Height Correctly Using Calipers
Beckstrand has found that many shooters aren’t inputting sight height or they are guessing at the correct height. As target distance increases, just a half-inch of sight height inaccuracy can mean several inches up or down.
“Sight height is the input most often overlooked and is usually the source of greatest error. I think a lot of shooters, especially those new to long-range shooting, simply don’t understand the importance of this input.”
Sight height is the distance from the centerline of the scope to the centerline of the bore. Some shooters, Beckstrand believes, just “eye it up” and estimate the distance. “Really, you should use a set of calipers to measure the sight height distance … within 0.1 inch”.
Get Leading Ballistics App for iOS Devices
Need a top-notch Ballistics App for your iPhone, iPad, or iPod? Start with Ballistic AE, the number 1 (i.e. most installed) App for iOS systems. Ballistics AE (Advanced Edition) is the most popular iOS ballistics program for many good reasons. Full-featured and easy to use, Ballistics AE has been refined over many years, and it supplies rock-solid solutions derived from JBM Ballistics solver (created by James B. Millard). Unlike some other Apps, Ballistics AE is STABLE on iPhones (with various OS levels). What’s cool is that Ballistics AE is now on sale for $12.99.
We’ve used the Ballistic AE program on an iPhone 5S, iPhone 6, and iPad, and it performed well. Here are some of the features we liked:
1. Mirrors output from online version of JBM Ballistics we often use for initial calculations.
2. Controls are simple to use and (mostly) intuitive.
3. Handy comparison feature lets you compare ballistics for different projectiles side by side.
4. Advanced Wind Kit allows you to account for complex wind situations.
5. Projectile and BC Databases are very comprehensive.
6. Software is regularly updated to match Apple OS changes.
Nosler’s line of RDF™ (Reduced Drag Factor) bullets feature very high Ballistic Coefficients, hybrid-type ogives, and tight, factory-closed meplats. Nosler’s RDF bullets were designed to be very competitive match projectiles for their respective bullet weights. Now offered in four calibers, Nosler RDF bullets genuinely deliver excellent performance for the price. Shooters, particular PRS competitors, have found the RDFs deliver the flat trajectory and high BC necessary to reach the podium.
Nosler is proud of its RDF bullets, which feature tight, uniform meplats: “Nosler knows what gives competitive shooters an edge, isn’t an edge at all. It’s a point. With the highest in-class Ballistic Coefficient and smallest, most consistent meplat, RDF is the flattest-shooting match bullet in its class. Now available in more calibers and weights, the RDF’s meticulously-optimized compound ogive and long, drag-reducing boat-tail make achieving peak accuracy a snap”.
Experience RDF, the Flattest-Shooting Match Bullet:
RDF bullets are also available in Nosler factory ammunition in a variety of popular cartridge types. Nosler factory ammo lets you spend more time at the range and less at your reloading bench. Look for RDF bullets loaded in Nosler’s “Match Grade” Ammunition. Below is the .264-caliber, 140 grain RDF loaded in 6.5 Creedmoor, a popular chambering for PRS and tactical shooters.
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Written by Sierra Bullets Ballistic Technician Paul Box
Judging by the calls I’ve had through the years, I think some shooters might be placing too much importance on Ballistic Coefficient (B.C.). The best example of this comes from a call I had one day. This shooter called wanting the ballistic coefficient of one of our Sierra bullets. After I told him he seemed a little disappointed, so I ask him what his application was. Long range target, deer hunting in the woods? Talk to me.
As it turned out, he hunted deer in open timber. He very rarely shot beyond 100 yards. I pointed out to him that, under 200 yards, B.C. has little impact. Let’s compare a couple of bullets.
Let’s look at the trajectory of a couple of bullets and see how they compare. The .30 caliber 180 grain Round Nose #2170 RN and the 180 grain Spitzer Boat Tail #2160 SBT. The round nose has a B.C. of .240, while the SBT is .501. Starting both bullets out of the muzzle at 2700 FPS [with a 100-yard ZERO], at 200 yards the #2170 RN impacts 4.46″ low while the #2160 SBT impacts 3.88″ low. That’s a difference of only 0.58″ in spite of a huge difference in Ballistic Coefficient. If we compare out at 500 yards, then we have a [significant drop variance] of 14.27″ between these two bullets. [Editor: That difference could mean a miss at 500 yards.]
Distance to Your Prey is the Key Consideration
In a hunting situation, under 200 yards, having a difference of only .58” isn’t going to make or break us. But when elk hunting in wide open spaces it could mean everything.
The next time you’re choosing a bullet, give some thought about the distances you will be shooting. Sometimes B.C. isn’t everything. If you have any questions, please give the Sierra Bullets technicians a call at 800-233-8799.
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Each Wednesday, the U.S. Army Marksmanship Unit publishes a reloading “how-to” article on the USAMU Facebook page. This past week’s “Handloading Hump Day” article, the latest in a 7-part series, relates to chronograph testing and statistical samples. We highly recommend you read this article, which offers some important tips that can benefit any hand-loader. Visit the USAMU Facebook page next Wednesday for the next installment.
Chronograph Testing — Set-Up, Sample Sizes, and Velocity Factors
Initial Chronograph Setup
A chronograph is an instrument designed to measure bullet velocity. Typically, the bullet casts a shadow as it passes over two electronic sensors placed a given distance apart. The first screen is the “start” screen, and it triggers an internal, high-speed counter. As the bullet passes the second, or “stop” screen, the counter is stopped. Then, appropriate math of time vs. distance traveled reveals the bullet’s velocity. Most home chronographs use either 2- or 4-foot spacing between sensors. Longer spacing can add some accuracy to the system, but with high-quality chronographs, 4-foot spacing is certainly adequate.
Laboratory chronographs usually have six feet or more between sensors. Depending upon the make and model of ones chronograph, it should come with instructions on how far the “start” screen should be placed from one’s muzzle. Other details include adequate light (indoors or outdoors), light diffusers over the sensors as needed, and protecting the start screen from blast and debris such as shotgun wads, etc. When assembling a sky-screen system, the spacing between sensors must be extremely accurate to allow correct velocity readings.
Statistics: Group Sizes, Distances and Sample Sizes
How many groups should we fire, and how many shots per group? These questions are matters of judgment, to a degree. First, to best assess how ones ammunition will perform in competition, it should be test-fired at the actual distance for which it will be used. [That means] 600-yard or 1000-yard ammo should be tested at 600 and 1000 yards, respectively, if possible. It is possible to work up very accurate ammunition at 100 or 200 yards that does not perform well as ranges increase. Sometimes, a change in powder type can correct this and produce a load that really shines at longer range.
The number of shots fired per group should be realistic for the course of fire. That is, if one will be firing 10-shot strings in competition then final accuracy testing, at least, should involve 10-shot strings. These will reflect the rifles’ true capability. Knowing this will help the shooter better decide in competition whether a shot requires a sight adjustment, or if it merely struck within the normal accuracy radius of his rifle.
How many groups are needed for a valid test? Here, much depends on the precision with which one can gather the accuracy data. If shooting from a machine rest in good weather conditions, two or three 10-shot groups at full distance may be very adequate. If it’s windy, the rifle or ammunition are marginal, or the shooter is not confident in his ability to consistently fire every shot accurately, then a few more groups may give a better picture of the rifle’s true average.
Lapua, maker of premium brass, bullets, and loaded ammo, has released a new, state-of-the-art Ballistics program that runs on smartphones and mobile devices. The all-new Lapua Ballistics Mobile App is the first mobile ballistics app utilizing the 6DOF calculation model. 6DOF refers to “Six Degrees of Freedom”, referring to the multiple variables the software calculates. As explained below, a 6DOF solver can account for 3 components of movement PLUS 3 components of rotation. Of course, as with other ballistics software, the Lapua Mobile App looks at Bullet BC, velocity, and cross-wind effects. This software can also account for subtle, extreme long range factors such as the Coriolis Effect.
Notably, the new Lapua Ballistics App includes a library of up-to-date bullet profiles based on extensive field tests with Doppler Radar. Having an ultra-sophisticated 6DOF solver combined with Doppler Radar data makes the Lapua Mobile App one of the most accurate ballistics Apps on the market. Lapua Ballistics offers the latest, Doppler-proven Lapua cartridge and bullet data for you to combine with your firearm and local weather information. The App also includes the option to define custom bullets.
The Lapua Ballistics App is available for Android and iOS smart phones and mobile devices free of charge. For more info, visit www.lapua.com/lapuaballisticsapp.
6DOF, the most accurate calculation method. Lapua cartridge / bullet information. Distance, wind speed and angle. outputs numerical, reticle, table and graph views, metric and imperial values. Set Point Blank-range to different sight-in distances and impact windows. Define custom bullets ( BC G1 or G7 and Siacci method), Pre-set max 4 powder temperature.Sight-in-POI, Coriolis calculation
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Here’s a significant new addition to our knowledge base for Long-Range shooting. Hornady has released a new Ballistics Calculator that employs bullet profiles derived from Doppler radar testing and 3D projectile modeling. Hornady’s Patent Pending 4DOF™ Ballistic Calculator provides trajectory solutions based on projectile Drag Coefficient (not static G1/G7 ballistic coefficients) along with the exact physical modeling of projectiles and their mass and aerodynamic properties. This new 4DOF (Four Degrees of Freedom) calculator also accounts for spin drift and the subtle VERTICAL effects of crosswinds.
We strongly recommend you watch this video from start to finish. In greater detail than is possible here, this video explains how the 4DOF System works, and why it is more sophisticated than other commercially-offered Ballistics calculators. There’s a LOT going on here…
Aerodynamic Jump from Crosswind Calculated
According to Hornady, the 4DOF Ballistics Calculator “is the first publicly-available program that will correctly calculate the vertical shift a bullet experiences as it encounters a crosswind.” This effect is called aerodynamic jump. The use of radar-derived drag profiles, correct projectile dynamics, aerodynamic jump, and spin drift enable the Hornady® 4DOF™ ballistic calculator to provide very sophisticated solutions. Hornady says its 4DOF solver is “the most accurate commercially available trajectory program … even at extreme ranges.”
“Current ballistic calculators provide three degrees of freedom in their approach — windage, elevation, and range — but treat the projectile as an inanimate lump flying through the air,” said Dave Emary, Hornady Chief Ballistician. “This program incorporates the projectile’s movement in the standard three degrees but also adds its movement about its center of gravity and subsequent angle relative to its line of flight, which is the fourth degree of freedom.”
Using Doppler radar, Hornady engineers have calculated exact drag versus velocity curves for each bullet in the 4DOF™ calculator library. This means the 4DOF™ calculator should provicde more precise long range solutions than calulators that rely on simple BC numbers or drag curves based with limited data collection points. Emary adds: “The Hornady 4DOF also accurately calculates angled shots by accounting for important conditions that [other ballistic] programs overlook.”
“This calculator doesn’t utilize BCs (Ballistic Coefficients) like other calculators,” added Jayden Quinlan, Hornady Ballistics Engineer. “Why compare the flight of your bullet to a standard G1 or G7 projectile when you can use your own projectile as the standard?” That makes sense, but users must remember that Hornady’s 4DOF projectile “library” includes mostly Hornady-made bullets. However, in addition to Hornady bullets, the 4DOF Calculator currently does list seven Berger projectiles, six Sierra projectiles, and one Lapua bullet type. For example, Sierra’s new 183gr 7mm MatchKing is listed, as is Berger’s 105gr 6mm Hybrid.
This Video Explains How to Use Hornady’s New 4DOF Ballistics Calculator
Using the 4DOF™ Ballistic Calculator:
The Hornady 4DOF Ballistic Calculator provides trajectory solutions based on projectile Drag Coefficient (not ballistic coefficients) along with exact physical modeling of the projectile and its mass and aerodynamic properties. Additionally, it calculates the vertical shift a bullet experiences as it encounters a crosswind, i.e. “aerodynamic jump”. The use of drag coefficients, projectile dynamics, aerodynamic jump, and spin drift enable the 4DOF Ballistic Calculator to accurately measure trajectories even at extreme ranges. It is ideal for both long range and moderate distances and is available for the low-drag precision bullets listed in the drop down menu of the calculator. For calculating trajectories of traditional hunting and varmint bullets using BCs (ballistic coefficients), you can use Hornady’s Standard Ballistics Calculator.
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Here’s a valuable web resource our readers should bookmark for easy access in the future. ShootForum.com offers a vast Bullet Database, which includes roughly 3900 bullet designs in all. We counted nearly 200 different 6mm bullets! The bullet info comes from the makers of QuickLOAD Software. Access to the online database is FREE. Most database entries include Caliber, Manufacturer, Stated Bullet Weight, True Bullet Weight, Length, Sectional Density (SD), and Ballistic Coefficient.* In many cases multiple BCs are provided for different velocity ranges.
The database is great if you’re looking for an unusual caliber, or you want a non-standard bullet diameter to fit a barrel that is tighter or looser than spec. You’ll find the popular jacketed bullets from major makers, plus solids, plated bullets, and even cast bullets. For those who don’t already own QuickLOAD software, this is a great resource, providing access to a wealth of bullet information.
Values for Changed Bullet Designs
Some of our readers have noted some variances with BCs and OALs with recently changed bullet designs. In general the database is very useful and accurate. However, as with any data resource this extensive, there will be a few items that need to be updated. Manufacturers can and do modify bullet shapes. Kevin Adams, one of the creators of the database, explains: “Thanks for mentioning this database. It took us a long time to collate this information and have agreement to publish it. Please keep in mind that individual batches of bullets will differ from the manufacturers’ stated standards. This is more a reflection on the manufacturers’ tolerances than the database ‘accuracy’. We will continue to add to the database as more manufacturers’ figures come available.”
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In 2016, Hornady will introduce new hunting and match bullets with high-tech, heat resistant tips. Hornady developed the new “Heat Shield” bullet tips after Doppler Radar testing showed that the Ballistic Coefficients (BCs) of old-style tipped bullets were degrading in flight in an unexplained manner. Hornady’s engineers theorized that the old-style plastic bullet tips were deforming in flight due to heat and pressure. Hornady claims this problem occurred with high-BC (0.5+ G1) tipped bullets from a variety of manufacturers. Hornady’s testers believed that, after 150 yards or so, the tips on high-BC bullets were actually melting at the front. That enlarged the meplat, resulting in increased drag.*
Consequently, Hornady developed a new type of bullet tip made from a heat-resistant polymer. Further long-range Doppler Radar testing seemingly confirmed that bullets equipped with the new tips did not suffer from the BC loss previously found. This allowed the bullets to maintain a higher, more consistent BC during the entire trajectory. The end result is a bullet with reduced vertical dispersion at long range (or so Hornady claims).
New Hornady ELD-X Hunting Bullets
For 2016, Hornady will bring out two lines of projectiles using the new tips. The first line of bullets, designed for hunting, will be called ELD-X, standing for “Extreme Low Drag eXpanding”. These feature dark red, translucent, heat-resistant tips. With interlock-style internal construction, these hunting projectiles are designed to yield deep penetration and excellent weight retention. Hornady will offer seven different ELD-X bullet types, ranging in weight from 143 grains (6.5mm) to 220 grains (.30 Cal):
NOTE: We don’t know if the stated BC values are based on drag models or actual range testing. These new ELD-X hunting bullets will be loaded into a new line of Precision Hunter Ammo for a variety of popular hunting cartridges.
New Hornady ELD Match Bullets
Along with its new hunting bullets, Hornady is coming out with a line of ELD Match bullets as well. Hornady’s engineers say the new molded “Heat Shield Tip” should be a boon to competitive shooters: “You can’t point up that copper [tip] as consistently as you can mold a plastic tip. With the ELD Match line, and the Heat Shield Tip technology… we now have a perfected meplat. These bullets allow you to shoot groups with less vertical deviation, or less vertical stringing, because the bullets are exact in their drag [factor].” There are currently four bullets in the ELD Match line:
Hornady will offer factory ammunition loaded with ELD Match bullets, starting with 6.5 Creedmoor ammo loaded with the 140gr ELD, and .338 Lapua Magnum ammo loaded with the 285gr ELD.
Better Tips Make a Difference — But other Factors Are Important
Hornady claims that its new Heat Shield Tips are more uniform than the meplats on conventional jacketed, hollow-point bullets. This, Hornady says, should provide greater bullet-to-bullet BC consistency than is possible with conventional, non-tipped bullets.
We have heard such claims before. Plastic tips are good, so long as they are inserted perfectly in the bullet. But sometimes they are crooked (off-axis) — we’ve seen that with various brands of tipped projectiles. Other factors will affect bullet performance as well, such as bullet weight, bullet diameter, and bullet bearing surface length. Even with perfectly uniform bullet tips, if bullet weights or diameters are inconsistent across a sample, you can still have accuracy issues (and pressure-related velocity variances). Likewise, if the bearing surface lengths vary considerably from one bullet to the next, this can increase velocity spread and otherwise have a deleterious effect on accuracy.
So, overall, we think Hornady has probably engineered a better bullet tip, which is a good thing. On the other hand there are many other factors (beyond tip uniformity) involved in long-range bullet performance. It will be interesting to test the new ELD Match bullets to see how they compare with the best hollow point jacketed bullets from other manufacturers.
MORE TECHNICAL DETAILS
* Hornady’s Chief Ballistician Dave Emary authored a technical report based on the Doppler Radar testing of a variety of tipped Bullets. CLICK HERE for Emary Report. Here are some of the report’s key observations and conclusions:
After early testing of prototype bullets it was observed that all currently manufactured tipped projectiles’ drag curves were convex, not concave and that abnormally low ballistic coefficients were being observed over long ranges. The drag was rapidly increasing at high velocities.
At this point extensive testing was done with all types of commercially-available tipped projectiles. They all exhibited this behavior to a greater or lesser extent depending on their ballistic coefficient and launch velocity. Most projectiles exhibited BCs relatively close to published values for 150 to 200 yards of flight. Beyond these distances they all showed BCs substantially below published values.
It was obvious that something was changing in the tipped projectiles to cause a rapid increase in drag at higher velocities. The drag increases were most noticeable from 100 to about 500 yards. Drag increases stopped at velocities below approximately 2,100 fps. This behavior was not observed with hollow point or exposed lead (spitzer) style designs. The problem magnified as the velocity was increased. The problem was worse for heavier, higher-BC projectiles that maintained higher velocities longer. After some consideration the answer was obvious and one that several people had wondered about for some time but had no way to prove their thoughts.
The tip of a bullet at 3,000 fps will see temperatures as high as 850 degrees F and decreasing as
the bullet slows down. These temperatures on the tip were a known fact. What wasn’t known was how long it would take at these peak and decreasing temperatures for the polymer tips to begin showing effects, if at all. As it turns out it is within the first 100 yards of flight. Currently-used polymers in projectile tips begin to have properties like rubber at approximately -65 to 50 degrees F and will melt at 300 to 350 degrees F, depending on the exact polymer.
All current polymer-tipped projectiles have tips that are at best softening and deforming in flight and under many circumstances melting and badly deforming. To cut through a lot of technical discussion the problem becomes worse at higher ambient air temperatures (summer) and higher launch velocities. Projectiles that have a high BC and retain velocity well see higher stagnation temperatures for longer lengths of time and have greater degradation of the tip. Simply put it is a heat capacity problem –temperature times time. This makes BCs for current tipped projectiles a rough average over some distance, dependent on atmospheric conditions and muzzle velocity, and does not allow the accurate prediction of downrange ballistics much beyond 400 yards.
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Berger has released two important informational updates for its line-up of bullets. First, the Ballistics Coefficients (BCs) have been updated for the vast majority of bullets Berger sells. In addition, G7 model BCs are being provided for most of the bullets. You will want to use the updated BC data, which is based on actual testing of recent production lots of bullets.
Second, Berger is now providing a dual twist-rate recommendation for most bullets. Berger is now lists a “minimum” barrel twist rate as well as an “optimal” twist rate. To get maximum long-range performance from your bullets, use a barrel with the “optimal” rate of twist.
CLICK HERE for the latest Berger Quick Reference Sheets with updated BCs and new Optimal Twist Rates. Eric Stecker, Berger President says: “We have tested every lot of bullets produced in the last several years to bring you these updated numbers for all of our bullets.”
Ballistic Coeffificent (BC) Updates with G7 Data
Berger notes: “We have updated all of our Ballistic Coefficients to be even more accurate.
Prior to 2008, all of Berger Bullets’ BCs were calculated using a computer prediction. Early in 2009, we began measuring BCs with live-fire testing. As a result, Berger’s BCs were updated and G7 BCs were also made available. This represented a dramatic improvement in the accuracy of performance data at that time. Since 2009, the BCs assessed for Berger Bullets have not been updated. As part of our ongoing effort to provide shooters with the best information possible, Berger has been testing every lot of bullets produced for the last several years. The result is updated and highly accurate running averages of BCs for recent production lots.
Here are some of the Updated BC Values for popular Berger Target (Match) Bullets:
G7 Form Factor Addition
Berger also added the G7 form factor to the Ballistics Quick Reference Sheet. The analysis of form factors can be very useful when considering a bullet’s long range performance potential. Going by BC alone can be deceptive since BC includes the weight and caliber of the bullet. Form factor indicates how much drag the bullet has, which is a very important consideration for all bullets of all calibers.
NEW Dual Twist-Rate Recommendations
Recommended twist rates for bullets are commonly listed as a single value, such as 1:12” (one rotation in 12″ of barrel travel). This may be overly simplistic. There is a big gray area of marginal stability in which bullets can fly with good accuracy, but with a reduced (i.e. sub-optimal) Ballistic Coefficient. Recognizing this reality, Berger is now listing two twist rates for each bullet it makes. The first is the minimum twist needed for good accuracy, which Berger has always recommended. The second is the new optimal twist rate, which is the twist that will stabilize the bullet to a level which achieves its full performance (BC) potential. CLICK HERE For more information.
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Applied Ballistics LLC will release updated editions of two popular resource books: Applied Ballistics for Long-Range Shooting (3rd Edition) and Ballistic Performance of Rifle Bullets (2nd Edition). Retail price is $54.95 for each title, or $94.95 if purchased together. Pre-orders are now being accepted with a $5 discount per book. You can pre-order the new editions through the Applied Ballistics store. The new editions are expected to ship by the second week of December.
Applied Ballistics for Long Range Shooting (ABLRS), Bryan Litz’s “Magnum Opus”, will have significant enhancements. New for the Third Edition is content on Weapon Employment Zone (WEZ) analysis. WEZ analysis is the study of hit percentage, and how that will be affected by the uncertainties in your environment. Existing academic material is augmented with modern experimental findings. The Third Edition also includes a CD-ROM disc with Applied Ballistics’ latest version of its ballistic software. NOTE: The third edition of ABLRS does NOT include the library of bullet data. That bullet library now exists as a separate reference book: Ballistic Performance of Rifle Bullets.
Ballistic Performance of Rifle Bullets — Data for 533 Bullets AND Rimfire Ammo
The updated, Second Edition of Ballistic Performance of Rifle Bullets contains the current library of all modern bullets tested by the Applied Ballistics Laboratory. Expanding on the First Edition, which had data on 400 bullets from .22 to .408 caliber, this Second Edition contains data on 533 bullets from .22 through .50 caliber. In addition to the centerfire bullet data, the Second Edition contains live fire data on 90 types of rimfire ammo which were all tested for muzzle velocity and BC through five different barrels of various twist/length configurations. This library of experimental test data is the most extensive and accurate resource ever assembled for small arms bullets. Numerous modern ballistics programs draw from the library of tested BCs that are published in this book.
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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.
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