Centerfire

Centerfire is a type of firearm cartridge in which the primer is seated in the center of the base of the cartridge case. When the firing pin strikes the primer, it ignites the primer's explosive compound, which then ignites the main propellant charge. This contrasts with rimfire cartridges, where the primer is distributed around the rim of the case base. Centerfire ammunition is the standard for most modern rifles and handguns, and is also used in many shotgun shells.

Construction and variants: The primer is housed in a centered pocket in the base, and two major primer designs are Boxer and Berdan. Boxer primers have a single anvil built into the primer cup, making reloading easier in many countries; Berdan primers use the case as an anvil with two flash holes, typically harder to reload. The cases are usually brass but can be steel, nickel, or coated. Centerfire cartridges come in rimmed and rimless base designs and in a wide range of calibers, from small pistol rounds to powerful rifle rounds.

History and current use: Centerfire cartridges were developed in the 19th century and gradually replaced rimfire designs for most purposes. The ability to place a robust primer in the center of the base enabled higher operating pressures, stronger cases, and convenient reloading. Today, centerfire ammunition dominates military, police, hunting, and sport shooting. Common examples include pistol rounds such as 9mm Parabellum and .45 ACP for pistols, .308 Winchester and .30-06 Springfield for rifles, and centerfire shotgun shells.