The Soviets developed the 5,6x39 as a hunting and 100 meter competition cartridge,
they just necked down their military 7,62x39 cartridge. Finland also used this cartridge
and SAKO produced small ring bolt action rifles known as the 220 SAKO.

US benchrest shooters took this to a higher level and delveloped the 22 PPC and 6mm PPC
as very accurate benchrest cartridges.

Final was the 6,5 Grendal cartridge

original 5,6x39mm had a 54gr bullet @ 2993 fps

photo shows 5,45x39, 5.6x39 and 7,62x39 P1010015_0011_011.jpg