Sectional Density?

[ninepointer]

Recently I've been hearing the term "sectional density" in discussions about bullet performance. Can someone please explain to me what "sectional density" is? Thanks

Ninepointer

 

[Tumbleweed]

In short, it's a ratio of mass and length - long (and therefore heavy) bullets in a given caliber have a higher sectional density than do short ones. Thus higher S.D.s encourage penetration.

For serious stuff where a lot of penetration is necessary, I prefer to use bullets with an SD of around .300 or better.

 

[ninepointer]

Thanks I just read a Chuck Hawks article on shotgun slugs, in which he described slugs as having poor sectional density.

http://www.chuckhawks.com/shotgun_slugs.htm

However, later in the article he talked about how slugs are very good (or notorious) for punching very deeply through brush thereby making slugs potentially more dangerous than rifles in crowded hunting situations (contrary to popular wisdom). If slugs have poor sectional density, how can they have deep penetration through brush? Is the article correct or contradictory? I'm confused

Ninepointer

 

[thebaron]

When a ferrari at top speed hits a hydro pole, it explodes into pieces (rifle bullet)
When a tank at top speed hits a hydro pole, the pole falls over and the tank keeps going (shotgun slug).

 

[Lefty Dick]

Think of it this way.
The SD for a 30 caliber 150gr. bullet is .226
The SD for a 270 caliber 150gr. bullet is .279
If you drove both bullets at the same velocity, and both bullets were of the same construction the 270 150 would out penitrate the the 30 cal 150.
So if you wanted to compare two different diameter calibers you would have to compare bullets of similar SD.
Such as 150, 270's= 160, 284's=180, 308's= 225, 338's but that's only if the bullets are constructed exactly the same.