Centerfire ammunition

A center-fire (or centerfire) is a type of metallic cartridge used in firearms, where the primer is located at the center of the base of its casing (i.e. "case head"). Unlike rimfire cartridges, the centerfire primer is typically a separate component seated into a recessed cavity (known as the primer pocket) in the case head and is replaceable by reloading the cartridge.

Centerfire cartridges have supplanted the rimfire cartridge, with the exception of a few small calibers. The majority of today's handguns, rifles, and shotguns use centerfire ammunition, with the exception of some .17 caliber, .20 caliber, and .22 caliber rimfire handgun and rifle cartridges, a few small-bore/gauge shotgun shells (intended mainly for use in pest control), and a handful of antiquated rimfire and pinfire cartridges for various firearm actions.

An early form of centerfire ammunition, without a percussion cap, was invented between 1808 and 1812 by Jean Samuel Pauly. This was also the first fully integrated cartridge and used a form of obturation employing the cartridge itself. Another form of centerfire ammunition was invented by the Frenchman Clement Pottet in 1829; however, Pottet would not perfect his design until 1855. U.S. General Stephen Vincent Benét developed an internally primed center-fire cartridge that was adopted by the U.S. Army Ordnance Department starting in 1868, ultimately being phased out in the mid 1880s.

The centerfire cartridge was improved by Béatus Beringer, Benjamin Houllier, Gastinne Renette, Smith & Wesson, Charles Lancaster, Jules-Félix Gévelot, George Morse, Francois Schneider, Hiram Berdan and Edward Mounier Boxer.

Centerfire cartridges are more reliable for military purposes because the thicker metal cartridge cases can withstand rougher handling without damage, and is safer to handle because explosive priming compound in a protruding rim is more likely to be triggered by impact if a rimfire cartridge is dropped or pinched. The stronger base of a centerfire cartridge is able to withstand higher chamber pressures which in turn gives bullets greater velocity and energy. While centerfire cartridge cases require a complex and expensive manufacturing process, explosive handling is simplified by avoiding the spinning process required to uniformly distribute priming explosive into the rim because of uncertainty about which angular segment of a rimfire cartridge rim will be struck by the firing pin. Larger caliber rimfire cartridges require greater volumes of priming explosive than centerfire cartridges, and the required volume may cause undesirably higher pressure spikes during the ignition process. Reducing the amount of priming explosive will greatly diminish the ignition reliability of rimfire cartridges, and increase the probability of a malfunction such as a misfire or hang fire.

Economies of scale are achieved through interchangeable primers for a wide variety of centerfire cartridge calibers. The expensive individual brass cases can be reused after replacing the primer, gunpowder and projectile. Handloading reuse is an advantage for rifles using obsolete or hard-to-find centerfire cartridges such as the 6.5×54mm Mannlicher–Schönauer, or larger calibers such as the .458 Lott, for which ammunition can be expensive. The forward portion of some empty cases can be reformed for use as obsolete or wildcat cartridges with similar base configuration. Modern cartridges larger than .22 caliber are mainly centerfire. Actions suitable for larger caliber rimfire cartridges declined in popularity until the demand for them no longer exceeded manufacturing costs, and they became obsolete.

The identifying feature of centerfire ammunition is the primer which is a metal cup containing a primary explosive inserted into a recess in the center of the base of the cartridge. The firearm firing pin crushes this explosive between the cup and an anvil to produce hot gas and a shower of incandescent particles to ignite the powder charge. Berdan and Boxer cartridge primers are both considered "centerfire" and are not interchangeable at the primer level; however, the same weapon can fire either Berdan- or Boxer-primed cartridges if the overall dimensions are the same.

The two primer types are almost impossible to distinguish by looking at the loaded cartridge, though the two (or more) flash-holes can be seen or felt inside a fired Berdan case and the larger single hole seen or felt inside a fired Boxer case. Berdan priming is less expensive to manufacture and is more commonly found in military-surplus ammunition made outside of the United States.