Paul--
You are quite correct in that the words I used were applied with generic "hunting" associations.

The accepted purpose of sectional density is to give a relative estimate of the potential penetration of similarly shaped projectiles with different masses moving at similar speeds.

Specifically SD is the weight of the bullet divided by the square of the diameter. It is the numerical representation of the bullets ability to carry its momentum forward .The higher the number the better the ability to linearly penetrate a medium with uniform frictional resistance.If I want deep penetration I want
more momentum acting thru a given bullet diameter than less momentum. At the same velocity that means more mass.

My generic referral to "momentum" is incorrect as well.How can we rate cartridges as "charge stoppers" ? How hard a "blow" does the bullet impart? The concept desired is basically the signfigance of the contact force vector on the contacted object.A larger surface contact area/momentum suggests a higher % of the force vector will be expended upon surface contact.The animal will percieve a "harder blow".

I personally feel SD has great utility and represents similarly fashioned bullets relative abilities to penetrate.

I must be old, cause I like it!!