AK vs M16

One of the major metrics of Cold War was comparing various things produced by two competing superpowers, one of these things were the main personal weapons of their armies, AK-47 (AKM) for USSR and its American rival M16. Lots was written on this topic and most of it completely off the mark. Differences in doctrine between Soviet and American armies make such comparison close to that of apples and oranges.

To begin with M16. It was created and adopted during Vietnam war and was American answer to North Vietnamese AKs, supplied by USSR. Main requirement was easiness of handling during automatic fire. Previous American main battle rifle was M14 that was accurate, reliable and capable of automatic fire, but had too small of a magazine and too much of a recoil to make automatic fire usable. M16 solved these issues even if was not perfect weapon in certain other regards. M14 was later reused as a sniper rifle.

While American response to AK-47 came from adopting rifle for automatic fire, then Soviets took completely different approach. AK-47 was inspired by German Stg 44, which came from MP 40 lineage and was more of a machine pistol (SMG) remodeled for rifle cartridges rather than a rifle. In a sense so is AK-47, it's not a rifle but more of an SMG or super compact machine gun. AK does not even have Russian word for rifle in its name, like for example SVD or other actual rifles do. It is clear that its creators did not saw it as a rifle at all.

Despite fulfilling similar roles in modern militaries, this different lineage is the reason for fundamental differences between AK and M16. Despite simplifications, M16 more or less maintains rifle like accuracy and handling. Its more expensive and somewhat more finicky and fussy. It's a precise tool for a well-trained soldier to do his job with accuracy and precision.

AK is different. It's far from precise or accurate, in fact most AKs are not even rifled at all, making their accuracy non-existent. Instead, its cheap, reliable and simple to use. It was not designed to hit targets accurately but to saturate the battlefield with bullets and kill with numbers not with precision, similar to SMGs or a shrapnel shot.

Why such radically different design philosophies succeeded at the same time and none managed to best the other one and force imitation?

The reason is different doctrines that Soviet and American military uses. Fundamentally American army is quality first and Soviet one is quantity first. Americans recruit but a few professional career soldiers who stay with military for decades if not for life. Americans train them these soldiers extensively, until they could do with great proficiency all that a solder should do. 

Soldiers like this need equipment to match to bring out their full potential. What use all the accuracy training on the firing range will be if the rifle they are issued is inaccurate? American military invests heavily in its soldiers, and it would be a waste to lose one due to inaccurate rifle or other subpar equipment. That is why Americans do not imitate USSR but instead make their assault rifles precise and accurate.

USSR went polar opposite approach. Instead of investing heavily into each individual solider, USSR invests in their numbers. To that end guns and other equipment should as cheap as possible, to afford more soldiers. 

Training is simplified or cut too. That way you can draft more and more civilians into military to replace losses and plug the gaps in defences. Because soldiers are poorly trained, weapons they are given has to be robust and fool-proof. It would be a waste if quarter of weapons will break due to mishandling. 

For the same reasons AKs are not rifles like actual rifles. Accuracy and rifling is wasted on soldiers who do not know how to aim anyway. 

One of the reason the USSR took this approach was Operation Barbarossa, where most regular units were surrounded in first days of war and surrendered, forcing Soviet government to recruit civilians and hastily train them to fight.

So how the AK, despite its glaring issues and deficiencies, somehow managed to become the most popular gun in the world? The answer is simple, accessibility. Sure, good army trains its soldiers well and makes sure they do not die pointless death. However, in real world, that is often impossible. Take Operation Barbarossa that forced USSR to make new soldiers as fast as possible. One may claim it's an outlying situation but is it really. 

Take for example an insurgency where civilians with no prior weapon experience decided to take up arms to fight against oppression, they will not be able to either afford a good battle rifle, not train well enough to make good use of it. That is why African warlords, and most rebel armies all use AKs.

Another issue is poverty. A poor nation might not want or able to spend decently on defence. In such a situation they much more likely to go for a bigger poorly trained army armed with AKs rather than smaller one with better training and weapons. As much as smaller better trained and equipped army might be able to make fast work out of disorganised mob with cheap noisy guns, most of the time it does not come to actual fight. Mere presence of armed mob either deters invaders or keeps population suppressed.

Does it mean AK wins? Of course not. Each of these guns were designed to solve their own particular problem so replacing one with another is like replacing apples with oranges. 

Democratic countries cannot transition towards Soviet model of mass army; the sheer number of losses such army takes in any conflict will effectively destroy the productive population on which democratic system is based. Thus, democratic world has no other choice but to stick to its current small but well-trained professional career armies as well as well-designed expensive, accurate state of art rifles and other equipment.

On the other hand, African warlords that have surplus of unproductive angry people, to have no real alternative to AK or other cheap gun options. Such is life. Thus, M16 and other Western European rifles will continue to compete with one another for contracts of wealth 1st world militaries and AK will supply the rest.