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Old August 29, 2005, 12:48 AM   #1
Join Date: March 4, 2005
Location: Phoenix AZ
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Lyman 48th edition Handbook Question.

In every load recipe in the top right hand corner there is 2 numbers I couldn't find out from the book what these numbers referred to.

Example on page 356 upper right corner says BC: .139
and right below it says................................SD: .130

Yeah i'm new to this...! I think SD= Sectional Density but i'm not sure.
BC=??? I have not..A.. clue... Does anyone want to enlighten me?
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Old August 29, 2005, 01:53 AM   #2
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BC=Ballistic Coefficient
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Old August 29, 2005, 01:53 AM   #3
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BC=balllistic coefficient of friction. i.e., how well the bullet flies through the air.
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Old August 31, 2005, 12:27 AM   #4
Smokey Joe
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Sectional density

S. D. of a bullet is its weight in pounds divided by the square of its diameter in inches. Well, so what??

This is what: "The higher the S. D. of a bullet in a given diameter, the heavier and longer that bullet will be. This is important to several factors, including the B. C. of the bullet. However, from a big game hunter's standpoint the most relevant measure of S. D. is that with all else being equal, the higher the S. D. of a bullet, the better its ability to penetrate."
Lyman's 48th edition Reloading Manual, pg. 105

Same source: "The ability of a bullet to retain its velocity is expressed as the ballistic coefficient. This is a measure of how aerodynamic a bullet is and how well it cuts through the air." The higher the number, the better the bullet slips through the air, and the less velocity it loses over a given distance.

Bottom line: All else being equal, longer, heavier, pointier-nosed bullets go through both air and targets better than shorter, fatter, rounder-nosed bullets. Simple, no?
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