During World War 2 there were a lot of high power rifle cartridges running around, Japanese 7.5, German 8mm, American 30-06, etc. but shortly after the war all of those were replaced (in NATO territory) by the new 7.62. Was something wrong with all these other cartridges that were probably in abundance like nobody's business that necessitated the adoption of a new round? Were some rounds knocked out for political reasons (IE not wanting to adopt the Nazi 8mm, because it was from an enemy nation)? The soviets for some reason insisted on sticking with an ancient rimmed cartridge well into and after the cold war so I can't even fairly discount the 303 on that basis.
You know, books have been written around that question. The Army went into WW2 believing that long range, accurate rifle fire was the most important thing. This came from the
1919 Superior Board Report on Organization and Tactics. The US exited WW1, about 60% of the causalities, if not more were due to artillery, and yet the Superior Board claimed what the Army needed was more sharp shooting riflemen!
You know, the US hit a causality rate of 65,000 men per month in WW2, and by the time you get to 1943, (as reported in the American Rifleman) Infantry Officers were keeping their rifle men from shooting at the enemy at distances over 300 yards. The reason was, the shooters could not hit anything, and the enemy would respond with artillery fire and kill some people! It took years to teach marksmanship and those guys who could shoot straight were piles of rotted meat and busted bones around year two. Post war there was a lot of discussion whether long range accurate shooting had any value on a battlefield.
But, if you ever encounter the "User", you will find that they like what they have, want something better, but only a little different, and will reject revolutionary change. What the Infantry School wanted, was something that had the power of the 30-06, but weighed as much as an M1 Carbine.
The 30-06 was too long for a good automatic or semi automatic rifle round. That extra half inch in length adds un necessary length and size to the weapon. The rim was thin, so the 7.62 round is more compact, and has a thicker rim. It was recognized at the time, that is WW1, that the 30-06 was not optimal for the powders at the time of its creation. Now the 7.62 round,, the powders of the era gave the velocities, at the desired pressures, and filled the case. No wasted air space.
I like the 308 Win, I would have voted for it, it is accurate, powerful, and but, given that we are not going to train the military to high levels of marksmanship, the long range accuracy and power of the cartridge is wasted. One bud of mine, a Vietnam infantry solider, he liked the combat load of the M16, he could carry 400 rounds, instead of 200 7.62, and he had on bad days, fired all 400 rounds! His engagement distances were short. Yes the 7.62 would penetrate trees and bushes better, but you had to be on the receiving end to know that.