The AK did have a distinctive sound to it. Can't say I can hear the difference now. Special operations people sometimes carried AKS and dressed as VC or NVA as a ruse when deep in Indian country. They stopped doing this by 1969-70 as both sides had M16s by then.
There was also an issue of using captured ammo in Vietnam. There was a program where 7.62x39 rounds were loaded with high explosive (C4 IIRC) and slipped into VC and NVA ammo caches. These generated enough pressure to blow the bolt into the face of the shooter. This was to break confidence of the VC and NVA using Chinese ammo. It was enhanced by somehow disseminating forged Chinese documents which said they knew about some exploding ammo. They told us about this when I arrived in Vietnam in 1968.
Bringing things back from Vietnam was a different story. If it was a legitimate war souvenir no problem. No US made weapons. When I left Vietnam in 1969 they took all E6 and below into a large room where you dumped all your carefully packed baggage. The MPS went through everyone's stuff. They even confiscated BA30s (D cells) someone had in their radio. The MPS did take a few guys in cuffs. For what I don't know.
If you had a legitimate war souvenir like a SKS you carried it on the plane (no ammo allowed) and the stewardess put it away for you.
There was also an issue of using captured ammo in Vietnam. There was a program where 7.62x39 rounds were loaded with high explosive (C4 IIRC) and slipped into VC and NVA ammo caches. These generated enough pressure to blow the bolt into the face of the shooter. This was to break confidence of the VC and NVA using Chinese ammo. It was enhanced by somehow disseminating forged Chinese documents which said they knew about some exploding ammo. They told us about this when I arrived in Vietnam in 1968.
Bringing things back from Vietnam was a different story. If it was a legitimate war souvenir no problem. No US made weapons. When I left Vietnam in 1969 they took all E6 and below into a large room where you dumped all your carefully packed baggage. The MPS went through everyone's stuff. They even confiscated BA30s (D cells) someone had in their radio. The MPS did take a few guys in cuffs. For what I don't know.
If you had a legitimate war souvenir like a SKS you carried it on the plane (no ammo allowed) and the stewardess put it away for you.