# sectional density question...soild vs jacketed

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by snake, Dec 8, 2010.

1. ### snakeWell-Known Member

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This is comparing the same say for example .458 win mag 500gr barnes solid v.s. a standard 500gr jacketed soft point in same caliber,does the SD change?

I hope this makes sense. Im curious to know if it changes due to bullet material make. We are talking same caliber and weight.

thanks for any help or clearification.

Mike

2. ### boomtubeWell-Known Member

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SD is a simple math ratio of weight and diameter, no more.

A solid copper or steel jacketed bullet of a given diameter and weight has the same SD as a thin jacketed hollow point with a soft lead core. Meaning SD tells us nothing useful.

3. ### EagletWell-Known Member

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You may calculate the SD (Sectional Density) of any bullet by dividing the weight of the bullet (in pounds) by the square of its diameter.

Example: a 30 caliber bullet of 180 gr.

Weight in lbs = 180/7000 = 0.0025714 lbs.

Square of its diameter = 0.308X0.308 = 0.9486

SD = 0.0025714/0.9486 = 0.271

As stated above, if the diameter and the weight are the same the SD is the same.

SD is important because it has a significant effect on penetration. The higher the SD the better the bullet will penetrate assuming equal things like bullet design, materials, impact velocity etc.

A 180 gr. 0.308 bullet will have better penetration than a 180 gr. 0.338 bullet. ( assuming many things being equal like design, impact velocity etc.)

SD for the 180 gr. 0.338 would be: 0.225

I hope that helps on getting a better understanding of SD.

Last edited: Dec 8, 2010
4. ### snakeWell-Known Member

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big help,thanks for the fast responses!

5. ### jwp475Well-Known Member

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The higher SD bullet does not always out penetrate a lower SD bullet of the same material and construction. Meplat and nose profile have a large bearing on penetration. Example solids made from the same material but with different nose shapes and profile. A 450 grain flat point mono metal solid in 458 caliber Will out penetrate a round nose 500 grain solid even at the same velocity. The flat point will shoulder stabilize and penetrate without the yaw and tumbling of the round nose.