When the West (US, UK and most of EU) created their new rifles at the hight of the cold war why didn't they choose to adopt the same calibre as the current Russian rifle 7.62x39mm? I would have thought that if during the battles of World War 3 troops took large enemy strongholds they would then have had use of the (tens of?) thousands of rounds of ammo stored there. As far as I'm aware there were virtually no rifles in the west either civvie or military that was chambered to fire Eastern block ammunition and I would guess the same in Russia. Was it ever a serious thought of the leading powers to use the same ammo as their potential enemies or was a different calibre chosen deliberatly to ensure enemy ammunition couldn't be used?