7.62x39, is the round used by the legendary AK-47. It’s a popular caliber today, thanks to the abundance of cheap ammo and the many different firearms that use the round; from the SKS carbine, to AR-15 conversions, to the Ruger Mini-30 rifle, 7.62x39 finds a home in many forms of firearm.
The development of this round started in the Soviet Union, in 1944, during WWII. At the time, the soviets were looking ahead for a sort of "do-all" cartridge that could be used over multiple weapon platforms to fill different roles in their armed forces, simplifying the process. The platforms they had in mind were the SKS, a carbine, the AK-47, a full rifle, and the RPD, a light machine gun.
Think back to the end of WWII, when the US had the M1 Garand, the Browning Automatic Rifle (BAR), and the M1919 series of machine guns, all of these weapon platforms used the same round, and to great effect.
The initial development ran from 1944 to 1947, going through minor changes throughout the 20th century. Almost all the 7.62x39 produced is steel cased, berdan primed, with corrosive primers.Steel cases and berdan primers are cartridge cases that cannot be reloaded.
Corrosive ammunition is supposed to have more reliable ignition in extreme cold, but the downside is that there are certain salts in the primers that are spread throughout the rifle when fired, and can then lead to rust. To avoid rust, after you finish shooting corrosive ammo, you need to clean your gun with something that can neutralize salts, like water, usually hot soapy water, to clean all the areas of your gun where any of the gas and powder residue may reside. In short, a lot more work than just cleaning your gun with oil and wiping it down when it gets dirty!
In 1962 the soviets adopted a subsonic "reduced speed" round that was longer and heavier than the standard rounds, however, this round is not available in the states outside the occasional handful of collectors rounds.
One of the main reasons to reload 7.62x39 is to create a round for hunting, or loading sub-sonic ammo for suppressed shooting. You’ll need brass cartridge cases, like the ones you can find at Capital Cartridge to do this.
7.62x39 held it’s position as the standard round for the Soviets until the 1970s when the AK-47 began being replaced by the new AK 74.