How do you find the G7 value for your bullet??
- Thread starter Raptor
- Start date
fullersson
B&B Gunworks bbgunworks.com
JBM doesn't have them listed for you? Not the G7 but the bullets that you use.
Raptor,
You might want to pick up a copy of Bryan Litz's book(s), Applied Ballistics for Long Range Shooting. In these (there's both a first and second edition) he has the G1 and G7 BCs for an entire range of bullets, Berger, Sierra, Nosler, Hornady, Lapua and a few others. It's a good read, aside from just this information, and will answer a ton of questions.
Aside from that, you can use a set of G7 tables to calculate the BC just as you would the G1, Ingalls, whatever. The classic Hatcher's Notebook has a complete section on how this is done, and includes a full set of Ingalls tables.
You might want to pick up a copy of Bryan Litz's book(s), Applied Ballistics for Long Range Shooting. In these (there's both a first and second edition) he has the G1 and G7 BCs for an entire range of bullets, Berger, Sierra, Nosler, Hornady, Lapua and a few others. It's a good read, aside from just this information, and will answer a ton of questions.
Aside from that, you can use a set of G7 tables to calculate the BC just as you would the G1, Ingalls, whatever. The classic Hatcher's Notebook has a complete section on how this is done, and includes a full set of Ingalls tables.
There is a formula in Bryan's book, it is rather complicated and I converted it to use in Excel. It does require accurate measurements of your bullet and a judgement call on the shape of the ogive.
Raptor,
There isn't a conversion, per se, it's simply a case of the same basic input information being used with two very different drag models. The G1 is actually a fairly blunt projectile, and not very aerodynamic. It's been the standard "default" drag model for virtually all industry bullet makers just to keep things simple and on an even field for comparison. The manufacturers know full well that this isn't an ideal drag model for the majority of modern bullet designs, but it's what's become the accepted norm. The G7 is much more streamlined, and equates to our modern match bullets much better. Bryan and Berger are slowly creqating a better understanding of the difference between the drag functions and the utility of matching the appropriate table with any given bullet design. Hey, it's a start. You might check out the Hatcher book I mentioned, since it has a complete set of Ingalls tables, along with a full explanation of their use. The Ingalls' projectile can be used interchangeably with the G1, with only very minor difference in the results. It's agood exercise, anyway, and makes for a better understanding of what you're looking at when you deal with a BC.
There isn't a conversion, per se, it's simply a case of the same basic input information being used with two very different drag models. The G1 is actually a fairly blunt projectile, and not very aerodynamic. It's been the standard "default" drag model for virtually all industry bullet makers just to keep things simple and on an even field for comparison. The manufacturers know full well that this isn't an ideal drag model for the majority of modern bullet designs, but it's what's become the accepted norm. The G7 is much more streamlined, and equates to our modern match bullets much better. Bryan and Berger are slowly creqating a better understanding of the difference between the drag functions and the utility of matching the appropriate table with any given bullet design. Hey, it's a start. You might check out the Hatcher book I mentioned, since it has a complete set of Ingalls tables, along with a full explanation of their use. The Ingalls' projectile can be used interchangeably with the G1, with only very minor difference in the results. It's agood exercise, anyway, and makes for a better understanding of what you're looking at when you deal with a BC.
In JBM, if the menu has your bullet with (Litz) written beside it, that will use G7 for the calculations. If no Litz BC, you need to use the G1 BC that is known or published.
Or get Bryan's book.
Or get Bryan's book.
As mentioned, Bryan Litz's book is a good read. I'd go so far as to predict that - in the long run - the facts presented in the 1st book will contribute as much to the popular knowledge base concerning LR shooting as the availability of accurate & affordable chronographs has to rifle shooting in general. Some will buy the book(s) just to get the bullet BC database (which is head & shoulders above anything else I've seen), but they're missing the boat if they don't take the time to read completely through the book. I've read & re-read the 1st book, and have been meaning to send off an order for the 2nd one, as Bryan has been hard at testing a great number of additional bullets in the time since the 1st edition was published.
TominSWNY said:
If you meant that for me, I did not receive it. If you meant it for someone else, please accept my apologies.
+1 on all who suggested buying Bryan's book - it's a treasure, as is the latest version of his external ballistics program, included on a CD with the 2nd edition. It can be ordered directly from him:
http://www.appliedballisticsllc.com
http://www.appliedballisticsllc.com
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