The 5mm Bergmann is an unusual centerfire 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

Extractor (firearms)

An extractor is a part in a firearm that serves to remove brass cases of fired ammunition after the ammunition has been fired. When the gun's action cycles, the extractor lifts or removes the spent brass casing from the firing chamber.-Overview:...

requiring a groove which produced a semi-rimmed case. The long bullet was inadequately stabilized and tended to tumble in flight.