The AK, short for Avtomat Kalashnikov, is one of the most widely produced rifles in history, with an estimated population of over a hundred million units worldwide. It spread because it is simple to build, cheap, and light enough to carry a long way. Mikhail Kalashnikov developed the original in the Soviet Union as a long-stroke gas-operated rifle chambered in 7.62×39mm; later variants shifted to 5.45×39mm.

The reliability comes from having very few moving parts. If there is a cartridge in the chamber, it fires, and it does that in heat, cold, rain, sand and mud. Accuracy past 100 meters is a known limitation, but in close-range engagements that trade-off has rarely mattered to the people relying on it.

Its adoption across third-world militaries and irregular forces was partly a function of logistics: the AK could be handed to fighters with minimal training and would still function. That spread, combined with licensed and unlicensed production across dozens of countries, is why so many distinct variants exist today.

Two of the AK-pattern rifles you are most likely to meet in a US gun shop are the Zastava ZPAP M70 and the WASR-10, and they are not the same class of rifle.

Zastava ZPAP M70

The Zastava ZPAP M70 is a semi-automatic rifle built on the Serbian M70 design, itself derived from the AK platform. Zastava Arms manufactures it in Serbia.