The 5.56x45mm round was very effective in its original 1:14 or even 1:12 offerings, but when the Marine Corp decided they needed a rifle and not a sub-machine gun...well the rest is history.

1:7 or 1:9 makes for a very accurate 5.56x45mm hose. However, it also makes really nice little 22 caliber holes instead of tumbling.

The Russians figured this out, and added a bubble in the bottom of the 5.45 round. This is why the Afghan fighters called it "poison" during the Russian Vietnam (invasion of Afghanistan). The long projo yaws dramatically upon impact because its destabilized.

Of course, the Russian military doctrine has always been (in the modern era) to attack en masse with SMGs. This means accuracy isn't as important as brute reliability and fire capacity.

We have a different tradition, and it conflicts with the entire "assault rifle" concept.

There is no reason why we could not adopt the Brit's old 280 round or the Scar Heavy for mass issue.