Lyman Reloading Handbook 49th Addition

[Madjack181]

I have a new Lyman reloading book, and going through it I see for the different bullet load charts there are two numbers in the top right hand corner of each chart.
One says BC: and the other says SD:.
Is there anyone familiar with this book and what do those numbers represent?
Thanks

 

[hammer24]

BC= ballistic coefficient. SD= sectional density. Both are basically measurements of the bullet's profile and how it's built.

 

[Madjack181]

Thanks. This is what I like about this. Learn new stuff everyday!

 

[Madjack181]

I get the Ballistic coefficient, but what useful knowledge is there in knowing the sectional density of the bullet?

 

[Broom_jm]

I get the Ballistic coefficient, but what useful knowledge is there in knowing the sectional density of the bullet?

Sectional density is a simple measure of a bullet's mass compared to its diameter. Presuming projectiles of uniform material and construction, a higher SD will result in better penetration. Back before tapered jackets and bonded bullets, SD was used to give a good idea of how well a bullet would penetrate and kill, particularly on tougher critters.

Think of it this way: If you have a 180gr piece of lead the diameter of a piece of spaghetti, it would have a very low SD and you wouldn't expect it to penetrate well. That same piece of lead, in a 30 caliber bullet will have a much higher sectional density and it will penetrate much better.

BC is effected by bullet shape, while SD is not.

 

[Madjack181]

And here I thought I was going to go all day without learning something. Thanks!

 

[kludge]

It's the other way around...

.277" 150gr bullet, SD=.279 (150gr is fairly heavy for a .270 Win)
.308" 150gr bullet, SD=.226 (150gr is fairly light for a .30-06)

longer and thinner for a given mass = higher SD
longer and heavier for a given diameter = higher SD

 

[Seancass]

It's been a while since I read it, but isn't all this covered in the book?