Quote Originally Posted by Husar View Post
I know it, I was asking about the same kinetic energy but with different mass and diameter, basically whether kinetic energy is the only factor or not.

Vuk and rvg seem to be saying that a bullet with higher mass and bigger diameter is superior to a smaller but faster bullet even when the kinetic energy is the same.
That is not what Vuk is saying. Sectional Density is the ratio of an object's mass to its cross-sectional area (Wiki link). It is what makes a needle penetrate skin better than a copy of the unabridged War and Peace. Heavier rounds tend to have a better sectional density. A 7.62 usually has superior SD to a 5.56. SD and velocity are the two most important factors in determining whether or not something will penetrate armour. Basically mass is important, but it needs to be concentrated into as small an area as possible.