The sectionnelle density is a major factor to calculate the capacity of perforation of a projectile. It is function of the mass of the projectile compared to its surface in contact with the body to be perforated.

More the projectile is heavy, narrow and long, more it is perforating. This is why the arrows of the long Arc English longer (and thus heavier) than the arrows traditional and equipped with points bodkin were able to perforate a punt armor or 10cm of oak. Same manner one uses this principle in the Obus arrow: its profile and frayed length and its uranium or tungsten heart depleted so as to have a very important mass compared to the diameter of the projectile. The “arrows” are generally out of alloy of Tungstène (as the carbide of tungsten) which is harder than the steel, or of the arrows whose heart is in Uranium impoverished denser than steel, and thus concentrating in its center more power (this material is however less powerful). Tungsten has a melting point of 3.400°C and boiling of 5.700°C. The Uranium impoverished has as for him melting to 1.130°C and a boiling point with 3.850°C but it with the advantage of being provided free. Tungsten is in addition twice harder than depleted uranium, with a hardness of 500 Vickers against 250 Vickers only for depleted uranium).

Density of materials for comparison: Water, 1; Steel, 7,8; Bronze, 8,4 to 9,2 according to the mixture; Lead, 11,3; Uranium, 18,7; Uranium depleted, 19,1; Tungsten, 19,3.