The .220 Russian (5.6x39mm) cartridge was developed in the late 1950's for deer hunting in Russia. It is a 7.62x39 cartridge necked down to hold a 5.6mm bullet. It was later adopted by Finland, and by around 1965 was being produced by SAKO & Lapua. When it was introduced to the United States, Sako, & later Lapua, brass was stamped ".220 Russian".
The .220 Russian was used as the parent case for the 6mm PPC cartridge.