The 6.5×50mmSR Arisaka is a semi-rimmed rifle cartridge with a 6.705 mm diameter bullet. It was the standard Japanese military cartridge from 1897 until the late 1930s for service rifles and machine guns when it was gradually replaced by the 7.7×58mm Arisaka.

A rim is an external flange that is machined, cast, molded, stamped, or pressed around the bottom of a firearms cartridge. Thus, rimmed cartridges are sometimes called "flanged" cartridges. Almost all cartridges feature an extractor or headspacing rim, in spite of the fact that some cartridges are known as "rimless cartridges". The rim may serve a number of purposes, including providing a lip for the extractor to engage, and sometimes serving to headspace the cartridge.