The image of troops using "spray and pray" tactics is disappearing from the playbooks of most armies. The AK-47, on full automatic, is increasingly being seen as a liability, even by its many enthusiastic users. Originally designed to allow poorly trained troops to deliver automatic fire, the 4.5 kg (10 pound, loaded with a 30 round magazine) AK-47 didn't have to be cleaned frequently, and could still fire even if covered with mud, sand or any other crud commonly encountered on the battlefield. But the AK-47 has flaws. The same design that makes it jam proof, also delivered poor accuracy. Moreover, the shabby sights on the AK-47 don't help much either. The design also trades reliability for the ability to quickly change magazines, or even operate the safety. But the main reason over fifty million AK-47s were built was because it did what it was designed to do very well. The AK-47 was the ultimate "spray and pray" weapon. But the AK-47 was the end of the line for a weapon design philosophy that began nearly a century ago.
Equipping infantry with lightweight automatic weapons began during World War I. In doing that, the Germans also took the lead in developing submachineguns, like the MP 18, a weapon that would eventually evolve into the modern assault rifle. By the end of World War I, about 30,000 MP 18s were in use. The MP 18 demonstrated the devastating effect of automatic weapons in the hands of infantry. The MP 18 fired the standard 9mm pistol round at the rate of 6-7 bullets a second, and used a 32 round drum magazine. The basic need was for a compact weapon that could quickly fire a lot of bullets. This gave the MP18 user a big edge in combat. The Germans kept developing this type of weapon and by World War II they had the MP 38 and MP 40. The short range (50-100 meters) of the 9mm pistol round prevented the Germans from attempting to rearm all their infantry with this weapon, because the troops often had to hit targets farther away.
It wasn't until they saw the Russians use similar weapons on a mass scale during World War II that the Germans realized that the short range of the 9mm pistol round was not as great a shortcoming as they thought. The Russians understood that for an attack, arming all the troops with submachineguns gave you so much firepower, that the enemy had a hard time shooting back at your advancing infantry. This was particularly useful in urban or trench warfare, where there were a lot of small scale (a dozen or fewer attacking troops) operations at short ranges.
Russia produced over five million of their 3.6 kg (8 pound) PPSh submachineguns. It used either a 35 pound box magazine (weighing 680 grams/1.5 pounds) or a four pound drum holding 71 rounds. That was 7-8 seconds worth of firing. The bullet used was a 7.62mm (.30 caliber) pistol round that moved at only about 516 meters (1,600 feet) per second. Catch one of these in the head, and you were dead. Anywhere else, and you would probably live. But with so many of these bullets flying around, multiple hits were more likely.
One thing the 7.62/25 PPSh round didn't have was penetration. You needed that in urban areas to fire through doors, floors and walls. The Germans overcame this by developing the StG-44 in 1943, which used a more powerful, 7.92mm, bullet. This weapon heavily influenced the design of the AK-47. The StG.44, like the AK-47, used a shorter (than the standard rifle), and about 20 percent lighter, cartridge that used a bullet that could still fire through walls and doors. The Russians combined the best features of the StG-44 and PPSh to produce the AK-47 after World War II. It was cheap, rugged, used a larger, more powerful bullet, and enabled green troops to generate a lot of firepower on the battlefield.
But war has changed. Better trained troops, with more accurate weapons (like the M-16/M-4/SCAR), are more likely to prevail. Even the Russians have long since abandoned the AK-47 for weapons similar to the M-16. But all those AK-47s out there still appeal to the ill-trained, impoverished and trigger happy young men eager to make their point with a hail of bullets.