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Question on bergers bc

 
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  #15  
Old 02-18-2009, 06:15 PM
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Re: Question on bergers bc

Thank you guys for your responses. That is great customer service.
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  #16  
Old 02-18-2009, 06:39 PM
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Re: Question on bergers bc

grit,
For the conditions you gave and the 6.5mm VLD at 2600 fps, there is 2.5" difference between trajectories predicted by the G7 BC (0.304) and the average G1 BC (0.595). That's about 1 click.

The difference isn't very much in this case. A big reason why the G1 and G7 predictions are so close is because most of the flight time is spent in the 3000 fps to 1500 fps window that the G1 BC is averaged for. That's why we chose that window, because it's typical of long range shots, and will result in the closer match to G7 predictions. Even though there's only 2.5" difference, the G7 prediction is more accurate. I'll take every little bit I can get.

On to the 30 cal 210 VLD...

The difference in predicted drop at 1500 yards between the G1 BC of 0.616 and the G7 BC of 0.315 is 10.3", or about 3 clicks.

In order to use your program that accepts multiple BC's, I recommend just using our single advertised BC. It will get you very close, as the comparisons above indicate. If you ever get a program that accepts G7 BC's, you can make direct use of the better referenced BC. Till then, the averaged G1 BC will get you very close.

As an experiment, you can try entering these velocity banded G1 BC's into your program for the 210 VLD to see how the results compare to the average G1 BC. Then you can use another program to compare the G7 BC predictions.

BC Velocity (fps)
0.580 below 1500
0.602 1500 to 2000
0.624 2000 to 2500
0.631 2500 to 3000
0.637 above 3000

I'm interested to see what you find. I don't have a program that accepts multiple BC's so really don't know how it will compare. I suspect the banded BC will be closer to the G7 prediction than the average BC, but it will be close.

Also remember that the manner in which the BC is presented and used (averaged vs banded, vs G7, etc) is important, but more important is how the data was gathered in the first place. Just because it's G7 or banded or whatever doesn't necessarily mean it will be more accurate. If the drag of the bullet was estimated, or the bullet shape changed since the makers tested for BC, or if for any reason the basic raw data is inaccurate, the BC will be inaccurate no matter how it's described.

-Bryan
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Bryan Litz
Ballistician

Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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  #17  
Old 02-18-2009, 09:20 PM
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Location: Utah
Posts: 1,377
Re: Question on bergers bc

Thanks Bryan. I am going to read your link now. I will let you know how the banded g1 #s change things.

Ok. The banded G1 #s were very close to the G7 #'s. The .616 average was great to around 1k. Then off up to 3/4 moa, then back on, then off... Interesting and educational.

Stop teasing us and get the new resources on the market! We'll buy 'em. Long as we can buy bread, we'll buy fancy bullets!

Last edited by grit; 02-19-2009 at 12:43 AM.
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