Tactics have changed since the old days. In WWII the mortality rate was higher due to the power of calibers such as the 8mm Mauser or .30-06 Garand. Pick out a guy, sight him in, shoot him.
Most of the people killed in ground combat during WW2 were done in by artillery and crew served weapons. The problem with lethality, as far as the individual infantryman was concerned, in WW2 was not about terminal ballistics, it was about getting the individual infantryman to engage the enemy at all with direct fire. Researchers during the war (SLA Marshall, notably) found that only about 20% of troops in combat even fired their personal weapons at all, much less fired accurately and inflicted casualties on the enemy. Two guys running a machinegun, four or five guys crewing a tank or other AFV, or similar had much higher rates of engagement (over 90% if memory serves me correctly) and consequently much more lethal effects on the enemy.
Tactics have changed much since then (though doctrine has). Training has changed, however, and explains why the number of troops who will fire their individual weapons at the enemy has increased dramatically since then.
Now it's more of how many rounds can you spit out acurately at a specific point. Hence the caliber .223 itself and weapons like the SAW. Keep the enemy's head DOWN while you go around and pump as many rounds as you want from the side. Power is not the key today.
Flanking attacks and fire and manuever predate the 5.56mm round by quite a while. They were, for instance, a central part of infantry doctrine for US forces in World War 2, explain why weapons like the BAR were adopted, etc.
As for 30-06, the only reason it was even in service during World War 2 was that McArthur, during his stint as CoS of the Army pre-WW2, vetoed, for financial reasons, the adoption of .276 Pedersen for the new Garand rifle (the cartridge it was originally built for) or one of the other small calibers army researchers had identified as superior for infantry use to .30-06. We tend to think of 30-06 as a some obviously superior classic, but the truth of the matter is that the army wanted to be rid of it by the late 1920s. Only the near bankruptcy of the US government during the Depression kept 30-06 in service because we had mountains of it left over from WW1.
As an interesting side note, .276 Pedersen is, ballistically, remarkably similar to 6.8mm Remington SPC (and the British 280/30 round, but that's a whole other issue), even if case dimensions are completely different.
As for the gas system, direct doesn't make much sense to me. That's the only thing I dislike about the AR-15 design. Not sure what Eugene had in mind.
I believe that with late 1950s/early 1960s technology, the direct gas system produced about the lightest action possible, which is why it was used.
). My .02, now I'll shut up on it.
