At the time that took place, it had been known since post WW1 that .30 caliber service rifles were not needed for battlefields, and that smaller calibers and lighter ammo was the way to go. But so much ammo had been made lots of post WW1 designs got rechambered or forced to used ammo .like 30-06 due to nothing more than using surplus stock, not effectiveness. I.E. the Garand was never intended as a .30-06 rifle.
Fast forward, WW2 reinforced that knowlege even more with guns like the STG-444 M1 carbine and such, the intermediate cartridge finds it's role. The AK gets developed postwar. The FN FAL gets designed in .280 British, but force fucked into being .308 because 'Merica!
Meanwhile after pushing .308 we do the whole project salvo thing and are all oh shit, small light bullets are the hot hot heat.
So full circle, if the Irish would have had AR-15's (61 predates the M-16) instead of FAL's they would have had more ammo, that ammo would have been more lethal (fleet yaw) and out of the M-16 more accurate with a longer max point target effective range, and so on and so forth.