[quote=@RoadRash]
Yeah, true story. Most of the 'Nam vets I ride with still refuse to own an AR-platform rifle, even though the weapons have been massively improved. The modern incarnations of the rifles are outstanding, but those originals were definitely shit-sandwiches. I'm actually planning on having Davis snag an AK sooner or later. In the close confines of a jungle, the accuracy differences between the AK and M16 are negligible. A max-effective range of 400m is still a good bit farther than you'll be shooting in the trees. 
[/quote]

Yeah, they're way better now. Hell, I own an AR-15, pony Colt out of the same factory turning out the M4's for the military, using the same processes. I passed up on an AK, the semi auto kind, or an SKS because I've seen the damage that East Bloc ammo does to a weapon when it's not thoroughly cleaned out (corrosive primers), and I decided that I didn't want anything more complicated than a bolt action Mosin if I was going to be screwing with that. Kept reasonably clean, the AR works just fine. With good magazines and decent quality ammo, not a problem.

Anyway, the Viet Cong also fielded a lot of different weapons that weren't standard. Old French weapons, stolen American weapons, whatever they had access to in the last twenty to thirty years. America supplied a lot of weapons to the ARVN, and that means those weapons show up elsewhere. But VC units also used older Chinese and Russian type weapons as well; Mosin Nagant carbines, SKS'es, and quite a few M1 carbines (because Vietnamese troops found these guns handier than full sized battle rifles like the Garand.) One can also reasonably expect to see BAR's and M3 grease guns and the like, though the BAR isn't necessarily the weapon of choice for a lot of Vietnamese. DP28's and their derivatives might well show up alongside RPD's, ditto with the various Russian and Chinese/Vietnamese knockoffs of the PPSH burp guns. The French stuff include MAT-49's, MAS-49's and MAS-36's, as well as their various machineguns like the Mle 1924-29, though these are probably running out of ammo...except, perhaps the MAT-49 which fires 9mm.

RPG-2's were popular too; they were reloadable and din't have much range, but hey, like the man said, it's a jungle.

In the Central Highlands though, American troops could expect to encounter a lot of NVA/VNAF as well as VC, and probably a uniformity of weaponry and good ammo supply among the local VC, thanks to the Ho Chi Minh Trail.