The two most common variants of the AK-47 are the AKM (this is the updated version of the AK-47 and the rifle that was put into widespread production and issuance) of Russia and the Type 56 of China. The AKM uses a gas operated rotating bolt, using the gasses produced by the bullet when fired to drive the bolt back and load another round. This allows the weapon to be fired in semi-automatic or fully automatic modes.
The AK-47 and most of its variants fire the 7.62x39mm round, a shortened variant of the standard rifle round used by the Soviets in World War II. Much like the rifle, the ammunition is also one of the most commonly used in the world, used by a variety of different weapons such as the Type-81 Assault Rifle and the RPK Light Machine Gun (itself a derivative of the AK-47).
| The following paragraph contains information that is of disputed validity.
Cited sources are encouraged.
An AK (the term will be used henceforth due to the mass of variants), like any weapon in a Zombie Outbreak scenario, has it's merits and it's disadvantages. The advantages of the AK are its durability, reliability in adverse conditions, as well as having easy up-keep, and the easy availability of its ammunition. However, the 7.62x39mm will not usually fragment in flesh like the 5.56x45mm NATO of the M16 Assault Rifle, and it is less accurate at "long" ranges, about 300 yards (274.32 meters). The 7.62x39mm loses its speed quicker, although the 7.62x39mm will cause more damage at long distances where the 5.56x45mm NATO will fail to break apart. It is also heavier than an M16 (11 pounds as opposed to the M16's 8 pounds) and it's ammunition is also heavier. And finally, it is less ergonomic and thus less comfortable to fire, further hampering it's accuracy.
The AK is common in the Middle East, Africa, Asia, Eastern Europe and South America as a military weapon. In most other societies though, the AK is likely restricted to a semi-automatic civilian version, if not completely banned altogether. Most modernized armies, including Russia, China and several Eastern European countries have replaced the AK entirely with newer and more accurate rifles.
If you do decide to use the AK against the undead horde, try to aim low, as the battle sights are meant for greater ranges. Due to the weapon's high recoil, keep the selector switch on semi-automatic mode, or try to keep your fire restricted to short bursts or else you will fire right over the heads of the undead, and waste valuable ammunition. If you are unsure of headshots, aim for their legs. The powerful round will likely severely damage muscle and bone, and thus restrict their movements and give you ample time to escape or give follow-up shots.