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 Sectional Density 
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 Post subject: Sectional Density
PostPosted: Sat Jul 12, 2008 8:24 am 
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Why does the shooting industry/sport calculate sectional density different than classical physics?

Whereas the SD of a given object is generally calculated by dividing the mass of the object by the cross section area. Determined by the orientation of the view.

In bullets I often see it determined by dividing the weight of the bullet in pounds by the diameter^2 in inches.

The weight vs mass conflict I can accept. (Grudgingly) Since most bullets will be used on or near the surface of the Earth. But, why change from the cross sectional area (pi*r^2) to D^2.

TIA

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PostPosted: Sat Jul 12, 2008 8:46 am 
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Follow-up note: A Wiki article will invariably come up while doing a search. This one is most curious. It uses a conventional physics formula in its body, but cites a Chuck Hawks article as it's source. Yet, Chuck Hawks uses the bullet type formula, unlike the formula in the text. :?:

I think the bullet formula was invented as a convenient way to compare calibers and masses of bullets. It really has nothing to do with the actual sectional density.

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PostPosted: Sat Jul 12, 2008 4:11 pm 
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I saw the title of this thread and perked up. "Hey!" I thought, "I'm not the only one in the group who knows about sectional density."

...Until Kona started reeling off formulas. Then it sort of changed to, "Erm. I thought I knew about sectional density, but really I just know that 1) it's generally good and 2) how to get more in a few circumstances." :lol:

Sorry, Kona. Can't help you there. Math makes my eyeballs spin and shuts down my brain.

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PostPosted: Sat Jul 12, 2008 4:53 pm 
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:D That's okay!! It keeps me in a job teaching others. :D

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