The SKS was originally designed in 1944 to replace the Mosin Nagant. It’s a semi-automatic rifle that fires the 7.62x39mm round, the same round as the AK-47, and is loaded with a ten round stripper clip. The SKS saw very limited action in World War II, not being issued until 1945, and afterwards it was overshadowed by the AK-47, which became the main service rifle for the Soviet military.
That being said, millions of SKS carbines were still made and used as both secondary weapons for the Soviet military and were widely distributed to Soviet allies. The carbine is well known for its reliability like the AK-47, and features a gas piston rod to cycle the action and a spring loaded bolt carrier.
Today, the SKS is widely available on the United States surplus market and is popular with U.S. civilians, while also being used by numerous countries and insurgent forces throughout the world as well.