Editing Hollow-point bullet (section)

== Mechanism ==
[[File:Halvmantlad.jpg|right|thumb|[[6.5×55mm Swedish]] before and after expanding. The long base and small expanded diameter show that this is a bullet designed for deep penetration on large game. The bullet in the photo traveled more than halfway through a [[moose]] before coming to rest.]]

When a hollow-point hunting bullet strikes a [[soft target]], the pressure created in the pit forces the material (usually [[lead]]) around the inside edge to expand outwards, increasing the axial diameter of the projectile as it passes through. This process is commonly referred to as ''[[Expanding bullet|mushrooming]]'', because the resulting shape, a widened, rounded nose on top of a cylindrical base, typically resembles a [[mushroom]].

The greater frontal surface area of the expanded bullet limits its depth of penetration into the target and causes more extensive tissue damage along the wound path. Many hollow-point bullets, especially those intended for use at high velocity in [[Centerfire ammunition|centerfire]] rifles, are ''jacketed'', i.e., a portion of the lead-cored bullet is wrapped in a thin layer of harder metal, such as [[copper]], [[brass]], or [[Carbon steel|mild steel]]. This jacket provides additional strength to the bullet, increases penetration, and can help prevent it from leaving deposits of lead inside the [[Gauge (firearms)|bore]]. In ''controlled expansion'' bullets, the jacket and other internal design characteristics help to prevent the bullet from breaking apart; a fragmented bullet will not penetrate as far.