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G1... G7... ??

 
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  #1  
Old 12-08-2009, 08:06 AM
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G1... G7... ??

I have been using LoadBase (cool program but way over my head in many places. I plan to fix that.) and I just received a couple of boxes of Berger 168 gr. VLD hunting bullets (7 mag were back ordered). I also use a little iPhone app for ballistics as well as LoadBase on a pocket PC (best way to go imho). All of them have references and data entry points for G1 - G7, etc

For instance:

The bullet box says:

G1 BC = .473
G7 BC = .242

BC I understand... G1 and G7 I'm not so sure. I assume that it's related to muzzle velocity and some other velocity downrange. Since this appears to be a standardized measurement I'm guessing it's yardage (or meters)? Not velocity though for each load there will be an equivalent velocity for an equivalent point in the trajectory.

Just curious...
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  #2  
Old 12-08-2009, 09:10 AM
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Re: G1... G7... ??

They are two different drag profiles. The G7 is a more accurate profile for the bullets that we are using. The G1 is older technology. Looks better, but not as accurate. If you have G7 #'s, use them.

Steve
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Old 12-08-2009, 09:12 AM
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Re: G1... G7... ??

Mike,
Please read this article.
It explains the difference between BC's referenced to the G1 and G7 standard.
If you have any further questions about referencing BC after reading that, please post back and we can help. That article should give you the main idea.
-Bryan
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Old 12-08-2009, 09:25 AM
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Re: G1... G7... ??

The LoadBase manual is real good also, I've been using the new Berger G7 numbers and they have been right on, no tweeking as long as you remember to toggle to G7.
I'm going to get Brians book, I'm thinking it may straighten things up in my brain also.
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Old 12-08-2009, 09:28 AM
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Re: G1... G7... ??

That will explain it much better than I.

Steve
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Old 12-08-2009, 10:50 AM
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Re: G1... G7... ??

Rocky,
a slight correction here; the G1 is no older than the G7. They were developed at the same time and by the same guy, E.D. Lowry of Winchester/Olin. The G1 has been the default drag model that has been in use ever since as sort of a compromise standard for everything, including more modern design bullets that don't accurately match the resulting trajectory shown by that model. Berger's trying to change that, and educate the current generation to use the proper drag model, and enjoy the benefits of a truly accurate trajectory prediction.

I'm sure Bryan's link explains a ll this in his usual detail!

A little history . . .

Kevin Thomas
Lapua USA
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  #7  
Old 12-08-2009, 05:15 PM
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Re: G1... G7... ??

Thanks Kevin. I think I Knew that but had forgotten, rings a bell anyway. G7 seems new.

Steve
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