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 to that 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 preferrable for flat-based bullets, while G7 is ordinarily a “better fit” for longer, boat-tailed bullets.
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.
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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SHOT Show 2013 kicks off in two weeks in Las Vegas. One of our top priorities is to talk with the bullet makers from Berger, Hornady, Lapua, and Nosler.
At SHOT Show 2012 we chatted with Berger Ballistician Bryan Litz about Berger’s popular line of Hybrid bullets. Berger now offers a wide range of Hybrids in multiple calibers and weights. In fact, for .30-Caliber shooters, Berger now offers six different Hybrid match bullets, with weights from 155 grains up to 230 grains. New .338 Cal Tactical Hybrids were released in 2012 and big .375 Cal, and .408 Cal Hybrids are in the works (read more below).
Bryan tells us: “The hybrid design is Berger’s solution to the age old problem of precision vs. ease of use. This design is making life easier for handloaders as well as providing opportunities for commercial ammo loaders who need to offer a high performance round that also shoots precisely in many rifles with various chamber/throat configurations.”
For those not familiar with Hybrid bullets, the Hybrid design blends two common bullet nose shapes on the front section of the bullet (from the tip to the start of the bearing surface). Most of the curved section of the bullet has a Secant (VLD-style) ogive for low drag. This then blends in a Tangent-style ogive curve further back, where the bullet first contacts the rifling. The Tangent section makes seating depth less critical to accuracy, so the Hybrid bullet can shoot well through a range of seating depths, even though it has a very high Ballistic Coefficient (BC).
In the video we asked Bryan for recommended seating depths for 7mm and .30-Caliber Hybrid bullets. Bryan advises that, as a starting point, Hybrid bullets be seated .015″ (fifteen thousandths) off the lands in most barrels. Watch the video for more tips how to optimize your loads with Hybrid bullets.
Berger is Developing New Large-Caliber and Hunting Hybrids
In related news, Berger announced that it will be offering a series of .338-caliber Hybrids. First Berger is reintroducing the Gen 1 .338 Cal, 300gr Hybrid bullet in Berger’s Hunting line. Berger will also be making a 250gr Hybrid Hunting bullet using the same type of jacket as the original Gen 1 300gr Hybrid bullet. In addition, Berger has released a .338 Cal 250gr Match Hybrid OTM Tactical bullet, along with a 300gr Match Hybrid OTM Tactical projectile.
More big bullets are on the drawing board. Our source says “.375 Caliber and then .408 Caliber are the next new calibers to be made at Berger”. These are in the design phase, and Berger needs to build a new machine, so the .375s and .408s will not be available until 2013 at the earliest.
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Report by Jeff Williams, AccurateShooter Correspondent
If you’ve visited BergerBullets.com lately, you’ve noticed that Berger Bullets has completely over-hauled and updated its website. The new website has a very handsome, clean layout. It is also faster to load and much easier to navigate. We give Berger an “A” grade for the new website.
On Berger’s home page you’ll find product descriptions, easy-to-use (smart-phone friendly) product buttons, pull-down menus for all four Berger bullet line-ups, recent news items, plus videos. Click “Links” to access a comprehensive list of reloading resources with a directory of shooting association websites. Click the Berger Bulletin tab to read current product status reports, technical articles, and shooting tips.
Redesigned Bullet Info Tables
The bullet product info pages are much easier to read now. Simple tables display all the bullets of a particular type (hunting, target, varmint, and tactical), organized by caliber and weight within calibers. You’ll find BOTH G1 model and G7 model Ballistics coefficients (BCs) for all the bullets in the tables, and recommended twist rates are listed.
Berger Twist-Rate Stability Calculator
The new Berger website also offers a handy Twist-Rate Stability Calculator that predicts your gyroscopic stability factor (SG) based on mulitiple variables: velocity, bullet length, bullet weight, barrel twist rate, ambient temperature, and altitude. This very cool tool tells you if your chosen bullet will really stabilize in your barrel. LIVE DEMO BELOW — Just enter values in the data boxes and click “Calculate SG”.
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There’s a lot of buzz about ballistics programs for smartphones. Those are handy, to be sure, but most people still need a solid, full-featured program to run on their home computers. Berger Bullets offers a sophisticated ballistics programs for MS Windows computers that works really well, and lets you print out results. Up-to-Date G7 BCs for Berger projectiles are built-in to the program, and the price is right — FREE.
The program is basic enough to be easy to use, but flexible enough to allow you to calculate custom ballistics for your rifle and load. The program accounts for all the basic external ballistic parameters including bullet BC and muzzle velocity, atmospherics, uphill/downhill shooting, etc. The output tabulates velocity, energy and time of flight as a function of range. Bullet path and wind deflection are displayed in your choice of inches, centimeters, MOA or MILS.
Instructions for Program
On the Berger Bullets Blog (1/26/2010), You’ll find a description of program features and a complete set of instructions. Here are instructions for the bullet variables: “The bullet inputs are straightforward. The BC can be entered in reference to either the G1 or G7 standard. You can find the G1 or G7 BC for your bullet either printed on the bullet box label, or on our products page. For accurate results, you should measure the muzzle velocity with a good chronograph. If you don’t have access to a chronograph, you can estimate the muzzle velocity based on your load data.”
Tips for Best Results
Bryan Litz includes tips on getting the most from the Berger Ballistics program. Some of Bryan’s suggestions will also help you when working with other ballistics software:
G1 vs. G7 BC: The accuracy of the ballistic solution is only as accurate as the inputs you give it. The advertised BCs for Berger bullets are established by actual field firing tests over long range and are very accurate. Using the properly referenced BC (G7 vs. G1) for the bullet you’re modeling is important. For any bullet with a boat tail, we recommend using the G7 BC.
Muzzle Velocity: Knowing your true muzzle velocity is important when calculating external ballistics. It’s best to measure your muzzle velocity directly with a chronograph.
Altitude and Atmosphere: If you want a truly accurate long-range trajectory prediction, you can’t ignore atmospheric effects. This is especially true the farther you get from standard conditions (sea level altitude, 59 degrees Fahrenheit, 0% humidity).
Scope Verification: It’s important to verify the most important link between the calculated ballistics and your point of impact: your scope. If the ballistics program calculates 30.0 MOA of drop for a particular shot, and you dial your scope to 30.0 MOA, are you sure it’s giving you exactly 30.0 MOA? In reality, many scopes have enough error in them to cause misses at long range. It’s important to verify the value of your scope clicks by firing groups at short range.
If you have further questions not answered on Berger’s Blog Page, email Bryan.Litz [at] bergerbullets.com. NOTE: If your computer won’t run the program, please download and install this Java update: http://www.java.com/en/download/index.jsp. This is a Windows PC program. You may have problems trying to run it on a MAC in emulation.
Story sourced by Edlongrange.
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One of the great things about our Shooters’ Forum is that many uniquely talented shooters share their knowledge and test findings. One of those experts is “bsl135″ aka Bryan Litz. Bryan is no ordinary “weekend warrior”. He graduated from Penn State with a degree in Aerospace Engineering. He then began a career as a missile design engineer at Wright-Patterson Air Force Base. He has written many ballistics programs and technical papers dealing with long-range flight dynamics of projectiles. Bryan is also a superb long-range shooter, holding an NRA High Master Classification. At this year’s NRA National Championships at Camp Perry, Bryan beat 258 other competitors to win the Palma Individual Trophy Match. Bryan shot a remarkable 450/26x, not dropping a single point.
Breaking News: Just today, Bryan won the Ohio State Midrange Championship, an iron sights event with 15 shots each at 300, 500, and 600 yards. Bryan shot a spectacular 450/39X. Again, Bryan didn’t drop a point and his X-count would make this a new National Record, pending certification. Congrats Bryan!
Bryan also has his own website with a number of authoritative articles. Topics include: Bullet Design, Meplat Trimming, Gyroscopic and Coreolis Drift, Palma Bullet Analysis, How Ballistics Programs Work, and Ballistic Coefficient Testing. CLICK HERE to visit BRYAN LITZ Website.
7mm Bullet BC Testing — Evaluating the Numbers
Bryan does a lot of testing for bullet-makers, evaluating the performance of various bullet types. One thing he has observed is that manufacturers’ published BCs may vary considerably even for two bullet designs that appear to be nearly identical. In our Forum, Bryan offered this interesting analysis of the 7mm Berger 180gr VLD and the similar 7mm JLK 180gr VLD:
“I’ve developed a repeatable procedure for test firing bullets to determine ballistic coefficient. If you get Precision Shooting Magazine, the March issue has one of my articles about test firing the Berger .30 cal 155gr VLD. Long story short, my test procedure uses acoustic sensors in 200-yard increments to measure time of flight out to 600 or 1000 yards. My BC measurements are repeatable to within +/- 2%, usually within +/- 1%.
I have tested several 7mm bullets. Of particular interest are the Berger 180gr and JLK 180gr bullets. If you look at these bullets side by side, it’s hard to tell a difference between them. I believe the JLK bullet dies were made from the same set of prints as the Berger VLD (Design by Bill Davis of Tioga Engineering). So … why would these bullets have different [published] BCs? They’re the same weight and the same basic shape [with very minor differences in OAL and bearing surface length]. This is just the kind of smoke and mirrors that makes shooters think there is something mysterious about BCs and exterior ballistics that’s beyond the realm of human understanding. I was pleased with the results of my testing of these two bullets: the BC is virtually the same, as expected. All is right with the world.”
Drag Models — G7 is better than G1 for long-range Bullets
Most ballistics programs use the default G1 drag model. Bryan 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 are the results of my testing for these two bullets:
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.
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.”
[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.]
Effect of Bullet Pointing
Bryan has also tested the effect of pointing bullets. He’s determined that this does have a positive (if small) effect on ballistics. Bryan writes: “I have measured the Berger 180 VLD in both nominal and pointed meplat configurations. Pointing the meplat from 0.059″ to 0.039″ increases the G7 BC from 0.337 lb/in² to 0.344 lb/in². This results in less than 2″ difference in 1000-yard wind drift (10 mph 90°). The improvement is small, perhaps negligible for standard decimal prone targets with large scoring rings. The improvement is more significant for F-Class targets with smaller scoring rings. That being said, I do point my own Berger 180 VLDs that I shoot in prone competition. It’s fast, easy, doesn’t hurt anything, and every little bit helps.”
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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.
Drag Models — G7 is better than G1 for Long-Range Bullets
Instructions for Program
