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Shooting & Reloading - Mausers, Big Bores and others >> Big Bore Rifles
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Gadge
.300 member


Reged: 02/05/04
Posts: 130
Loc: Gippsland, Victoria, Australia
Re: SD Sectional Density ???
      19/07/05 08:00 PM

It's actually a roughish [inexact due to absence of some arithmetical factors, and odd units of measurement] expression of the weight/cross-sectional area ratio.

Obtained by dividing the bullet weight [lbs] by square of diameter [inches].

So for a given diameter, a heavier bullet will be longer [natch] and have a higher SD. And lose velocity [and hence energy] less over distance, than a lower SD bullet.

It's used really as a rough approximation for Ballistic Coefficient, which has to be measured as change in velocity with distance. And is dependent on a lot of external variables like starting velocity, air density, yada yada. This one expresses the bullet's drag function, as a proportion of that of a particular standard test bullet. So nose shape is taken into account here.

Any of the ballistics software packages around can calculate SD. You can do it on a calculator, as Bullet Wt [grs]/(7000xDiam^2[in])



--------------------
Cheers,
Doug

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Entire topic
Subject Posted by Posted on
* SD Sectional Density ??? SafariHunt 19/07/05 06:18 PM
. * * Re: SD Sectional Density ??? 4seventy   19/07/05 10:20 PM
. * * Re: SD Sectional Density ??? Boomer   20/07/05 12:46 AM
. * * Re: SD Sectional Density ??? atkinson6   30/07/05 09:27 AM
. * * Re: SD Sectional Density ??? 4seventy   30/07/05 09:49 PM
. * * Re: SD Sectional Density ??? Gadge   19/07/05 08:00 PM

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