I was told,as fact, that the Vietcong would scour the battlefields for the NATO ammo, and could fire it, single fire, from their Soviet Bloc bolt action rifles. As the NATO round did not have a rim, after firing it, to extract the shell casing, they used a cleaning rod, and would knock the spent casing from the chamber.
Don't think so. You're not going to get a 308/7.62 to fire in a Mosin. Look at the case dimensions.
What is true about that fact is the VC did scour the battlefields for ammo or any thing else they could find. GIs were big on throwing crap away and loosing stuff.
They didn't pick up 308s to fire in Mosins, they picked up 308s to fire in 308 rifles, which they did have, 308, 30-06, 30 cal Carbines, and even 5.56, because they had those rifles. The got those rifles from the ARVN troops. Mainly after a battle with ARVN troops.
It wasn't until the NVA got fully involved that they started standardizing their weapons. But even then they scrounged everything they could get their hands on.
This isn't an new concept, its been that way in every war. Indians didn't pick up 45-70s to shoot in their bows, they picked it up to shoot in their Springfield rifles.
Same way now, enemy troops pick up 5.56 to shoot in their captured 5.56 rifles.
Heck the British picked up 8mm stuff in WWI, not because they shot them in their Enfields, but to shoot in the German sniper rifles the picked up.