It should be no surprise to see the AK-47 on this list. The AK variants are simply the most popular firearms ever made. In fact, there are more AK-47s, AKMs, and AK-74s in circulation worldwide than any other firearm. The original AK-47 was a 7.62x39mm assault rifle with selective fire capabilities. It served as the standard rifle for the Soviet army. It later developed into the improved AKM and then the AK-74, which fires the ballistically more accurate 5.45x39mm.