The AK-47 is a Russian assault rifle designed in 1947 by Mikhail Kalashnikov and first used in 1949. It and an updated version called the AKM were used by the Soviet Union's Military (which was called the Soviet Army). It was later replaced by the AK-74. The AK-47 quickly became famous and spread all around the world because it was simple to fire, clean and maintain, and also because of its reliability. The AK-47 and its successors continue to be used by many of the world's armies. Many terrorist and insurgent groups also use the AK-47. It is a cheap, reliable, and easy to use weapon. The AK-47 was also available with a folding stock, the AKS-47, and a shortened version with the AKS74 folding stock, the AKMSU (used by armoured vehicle crews), although this was soon replaced by the AKS74U, which fires the 5.45 cartridge of the AK-74. There was also a light machine gun variant with a longer barrel and different shaped stock called the RPK.
The AK-47 uses Gas-operated reloading. When the bullet is moved down the barrel, a little bit of the gas behind the bullet is made to go up a small tube that pushes away the bolt. This is special because the person who is shooting the gun does not have to reload with their hand every time that they want to shoot - the gun reloads by itself.
The AK-47 used many simple ideas that were first invented for the German Sturmgewehr 44 WW2 assault rifle. The AK-47 is a common gun used by many groups because it is so cheap and available. One of the reasons it is so common is that the Soviets left many behind when they left Afghanistan in 1989 after invading it in 1979. The letters AK stand for Avtomat Kalashnikova, which is Russian for Kalashnikov's Automatic Rifle. It shoots the Soviet 7.62x39mm cartridge. It is only accurate up to 300 meters. After that the bullet starts to tumble and drop.