When Soviet firearms designer Sergei Simonov developed the SKS during the final years of World War II, military rifles looked very different than they do today.
Most soldiers still carried full-size bolt action rifles.
The SKS introduced something new: a lightweight semi-automatic carbine chambered in the then-new 7.62×39 cartridge.
It offered faster follow-up shots, softer recoil than full-powered battle rifles, and exceptional reliability under harsh conditions.
Although it would eventually be overshadowed by Mikhail Kalashnikov's AK-47, the SKS never disappeared.
Instead, it quietly became one of the most widely produced military rifles in history.
More than 15 million SKS rifles were manufactured by countries including the Soviet Union, China, Yugoslavia, Romania, Albania, East Germany, and North Korea.
Today, thousands of those rifles are still running exactly as they were designed decades ago.
That's an incredible testament to Simonov's engineering.