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Centerfire ammunition
A centerfire cartridge is a cartridge with a primer located in the center of the cartridge case head. Unlike rimfire cartridges, the primer is a separate and replaceable component.
Centerfire cartridges have supplanted the rimfire variety in all but the smallest cartridge sizes. With the exception of a few .17 caliber and .22 caliber pistol and rifle cartridges, small-bore shotgun cartridges (intended for pest-control), and a handful of antique, mostly obsolete cartridges, almost all pistol, rifle, and shotgun ammunition used today is centerfire.
==Advantages==
Centerfire cartridges are more reliable for military purposes, because the thicker metal cartridge cases can withstand rougher handling without damage. Centerfire cartridges are safer to handle; because explosive priming compound in a protruding rim is more likely to be detonated by impact if a rimfire cartridge is dropped or pinched. The stronger base of a centerfire cartridge protects the central primer from side impact, and is able to withstand higher pressures than a thin rimfire cartridge. Higher pressures give a bullet higher velocity and greater 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 an undesirably high pressure during ignition. Reducing the amount of priming explosive would reduce the reliability of rimfire cartridge ignition, and increase the probability of misfire or dud cartridges.
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 mostly 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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