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G1 or G7

 
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  #1  
Old 04-09-2012, 11:21 AM
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G1 or G7

can someone explain to me the difference between a G7 B.C and a G1 B.C
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"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
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"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
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My guess on W3P .308 230 Grain Bullet: G1 .740-.755
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  #2  
Old 04-09-2012, 02:17 PM
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Re: G1 or G7

They're merely different drag models used for predicting ballistic performance of a given bullet. The G1 is the "standard" bullet used throughout the industry, despite the fact that it's a relatively poor fit for most of our more modern projectiles. It's relatively short (about three calibers in length), flat based, and has a rather blunt ogive. In the absence of anything denoting some other drag model, you can usually correctly assume that a manufacturer's listed BC is based on the G1 model. Berger (or more specifically, Bryan Litz) has lead the charge to use the G7 drag model for the more modern designs. The G7 model is significant;y more streamlined, has a boat tail and more accurately represents the flight characteristics of modern VLD or OTM Match bullets we use today. The result of this is that a ballistic program using the G1 model for a trajectory calculation will see some significant variation downrange, from what is calculated. The farther downrange, the more that discrepancy will grow. For a bullet more similarly shaped to the G7 model, the calculated trajectories will be far more accurate when compared to the actual firing results.

There's several other drag models in this same series (E.D. Lowry's, developed in the late 1940's or early 1950's) that may be more appropriate for some other given bullet, say, a flat-nose .30-30 design or a LSWC pistol bullet, but they see very little use outside some professional circles. Hope that helps a bit, but believe me, this is a very (VERY) abbreviated explanation of a rather complex topic.
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  #3  
Old 04-09-2012, 02:42 PM
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Re: G1 or G7

thank you that helps, i understand it better now
__________________

I'm 16
"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
~George Washington

"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom

Biggest fail of 2014 so far... http://www.longrangehunting.com/foru...ea-ftf-128972/

My guess on W3P .308 230 Grain Bullet: G1 .740-.755
Reply With Quote
  #4  
Old 04-09-2012, 02:45 PM
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Re: G1 or G7

In addition to Kevins response, you can refer to this article:
Berger Bulletin A Better Ballistic Coefficient

And if you want the full story:
Book

The book explains G1 vs G7 in detail, as well as lists the measured G1 and G7 BC's for 225+ common long range bullets.

My 'short summary' is: G7 BC's have less variation over long range. A G1 BC may vary over 20% from muzzle to a long range target which makes it very difficult to predict a trajectory that's accurate all the way. A G7 BC typically has less than 5% variation over long range. The reason is because the G7 standard is a better fit for modern bullets. So it's naturally more predictive over long range than the less representative G1 standard.

-Bryan
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  #5  
Old 04-09-2012, 02:57 PM
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Re: G1 or G7

i went to bergers website and read bryan litz's explanation on it and that helped a lot
__________________

I'm 16
"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
~George Washington

"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom

Biggest fail of 2014 so far... http://www.longrangehunting.com/foru...ea-ftf-128972/

My guess on W3P .308 230 Grain Bullet: G1 .740-.755
Reply With Quote
  #6  
Old 04-09-2012, 03:29 PM
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Join Date: Mar 2012
Location: ND
Posts: 2,741
Re: G1 or G7

Thanks Bryan i didnt see your post when i posted. You posted it as i was reading it
__________________

I'm 16
"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
~George Washington

"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom

Biggest fail of 2014 so far... http://www.longrangehunting.com/foru...ea-ftf-128972/

My guess on W3P .308 230 Grain Bullet: G1 .740-.755
Reply With Quote
  #7  
Old 04-09-2012, 05:40 PM
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Join Date: Feb 2012
Location: Remington County, PA
Posts: 383
Re: G1 or G7

To put it simply, it is the air-drag-only model, that factors the sectional density of a bullet OUT of it's BC. At least that's the way I understand it.

Last edited by Max Heat; 04-09-2012 at 06:40 PM.
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