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  #1  
Old 01-28-2010, 7:06 PM
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Default Lower G7 BC at higher velocities? Experimental drag and G7 BC data for 175 SMK?

In the Litz book, Applied Ballistics for Long Range Shooting there is a section in the back that shows the drag and bc data for specific bullets and includes diagrams of the bullets. Can someone explain to me why it states that the G7 BC of 175 SMKs going at 3000fps(.240) is lower than at 2500 fps(.242)?
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Old 01-28-2010, 7:25 PM
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Just because. Accept it.
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Old 01-28-2010, 7:30 PM
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Quote:
Originally Posted by Teletiger7 View Post
In the Litz book, Applied Ballistics for Long Range Shooting there is a section in the back that shows the drag and bc data for specific bullets and includes diagrams of the bullets. Can someone explain to me why it states that the G7 BC of 175 SMKs going at 3000fps(.240) is lower than at 2500 fps(.242)?
I haven't read the book, but .002 difference in BC could just be experimental error and not significant.
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Old 01-28-2010, 8:07 PM
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Aerodynamics. As speed increases the shape (overall, frontal and BT) may not flow air as well as at the slower speed. Same as why the listed BC's are lower at lower velocity. The shape performs best within a specific range.
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Old 01-28-2010, 9:09 PM
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I haven't read the book, but .002 difference in BC could just be experimental error and not significant.
yep.
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Old 01-29-2010, 5:04 PM
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We're conditioned to think that 'BC degrades with velocity'. This is almost always true with the traditional G1 BC's because the drag curves mismatch so severely. In particular, the drag of most bullets grows in relation to the G1 standard below about 2000 fps.

However, since the G7 standard drag curve is so similar to most long range bullets, the drag curve of your particular bullet may be slightly above or below the G7 standard curve over a range of speeds. Because the curves ride so close together, you may find the BC increases or decreases slightly at various speeds.

Of course when you're talking about 0.002 difference (less than 1%), it could very well be experimental noise

Take care,
-Bryan
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Old 01-29-2010, 7:09 PM
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Thats what I thought....JK...Its nice to have the author on here....
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Old 01-29-2010, 10:42 PM
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Bryan,

Thanks for the response. I get what you are saying. Really cool to have the author of the book respond in this thread. BTW, great book. I really enjoyed the parts about wind deflection and spin drift.
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