Penetration
How deeply a bullet drives into the target, governed by its construction, weight, sectional density, and velocity at impact.
Penetration measures how far a bullet travels into the target before it stops, one of the headline figures in terminal ballistics. It is driven by the bullet’s momentum and by how well it holds its shape, so weight, sectional density, and the retained velocity at the moment of impact all feed into the result.
Construction often matters as much as the numbers. A monolithic bullet that stays intact and keeps a narrow frontal area will out-penetrate a softer bullet that mushrooms wide or fragments, even at equal weight and speed. Hunters balance penetration against expansion: too little stops short of the vitals, while too much can pass through without transferring enough energy.