The 5mm Bergmann is an unusual
centerfire
Two rounds of .357 Magnum, a centerfire cartridge; notice the circular primer in the center
A centerfire cartridge is a firearm metallic cartridge whose primer is located at the center of the base of its casing (i.e. "case head"). Unlike rim ...
cartridge produced for very early self-loading pocket pistols. The case is steeply conical and
headspaces on the conical case walls. Early versions (sometimes called the 5 mm Bergmann Rimless) were made without any rim or extraction groove; and relied upon blow-back for expulsion of the fired case from the chamber. Later Bergmann pistols provided an
extractor requiring a groove which produced a semi-rimmed case. The long bullet was inadequately stabilized and tended to tumble in flight.
References
Pistol and rifle cartridges
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