All three main power blocks have adopted similar sized small bore infantry weapon ammunition - but many combatant forces in Afghanistan's prolonged agony have swapped their small & light tools for heavier longer range capability rifles to try counter the hostile local & 'insurgent' forces.
Do we have a Goldilocks situation here - with the porridge (caliber), chairs (magazines), and beds (the delivery systems) .. Too hot - too cold, too heavy - too light, too long - too short range?
Riflemen and military folk will be aware of intermediate 6.5mm and 6.8mm caliber military trials - if not the post war British .280" (7.2mm). EM2 rifle.
EM-2 Bullpup .280" Caliber. - Adopted in 1951 But Dropped To align With NATO.
Caliber and 'Stopping Power' are at the heart of many regular heated discussions.
I'm truly not setting 'HOMEWORK' but many of you will find this (linked) report called 'BITING THE BULLET' a fascinating read about where our military should be going:
Look - it's only 22 pages with lots of pictures eh.
The Serbian Military may be the first of many to "bite the bullet".
Serbian Zastava AK-type 6.5 Grendel.