coloradojones

Question for you ammo experts: What exactly is sectional density and how does it affect bullet performance?

eldeguello

Sectional density is a comparison of the weight of the projectile, to its diameter. It is derived by dividing the weight of the bullet in grains by 7000 to give the bullet weight in pounds (7000 grains/pound), then dividing this number by the SQUARE of the bullet diameter (in inches).

All else being equal, (bullet construction, shape, and impact velocity), the higher a bullet's sectional density, the deeper it will penetrate in a given substance.

Sectional density is one of the two factors you must know (form factor, or coeeficient of form being the other)in order to compute a projectile's ballistic coefficient (ability to overcome air resistance). This figure tells you how fast a bullet will lose its initial velocity, compared to an arbitrary standard projectile.

Larry

stubblejumper

Bullet construction actually has a much larger effect on penetration than sectional density.A premium 140 gr bullet(such as the nosler partition) will usually penetrate as well or better than a conventional 175gr bullet which has a much higher sectional density.

Edited by - stubblejumper on 02/22/2002 21:19:18

handloader1

You can have the higest sectional density in the world, but if the bullet dosen't stay together through impact, high sectional density it is useless. Good Luck.

Edited by - handloader1 on 02/22/2002 00:19:26

Deleted User

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Briman

In theory with all other things being equal- construction, mass, and velocity, the bullet with the higher sectional density will penetrate further into whatever medium its being shot into.

eldeguello

DG, the shape and size of THE FRONT OF a BULLET has NO EFFECT ON ITS' SECTIONAL DENSITY. The ONLY two factors which determine sectional density are: bullet weight and diameter. A short, fat, round-nose, 180-grain .308" bullet has EXACTLY THE SAME sectional density as a long, sharp-pointed 180-grain .308" bullet!!

stubblejumper

Briman-A bullet test in the june 98 edition of handloader magazine compared speer grand slams in .308 caliber for penetration.They tested the bullet in 150,165,180 and 200 gr weights and although the 150's did penetrate a little less there was no difference between the 165,180 and 200 gr bullets as far as penetration was concerned.Apparently where premium bullets such as the grand slams and partitions are concerned the heavier bullets with higher sectional densities do not offer any real penetration advantage over lighter bullets of the same construction.My own results when using the nosler partition on elk and moose have shown results similar to the handloader tests.

Edited by - stubblejumper on 02/22/2002 21:29:14

Briman

I guess like most things, there is a big difference between theories and what actually happens in the real world.<img src=icon_smile_wink.gif border=0 align=middle>