This 1968 film, the only Vietnam War film apparently made during the conflict, starred John Wayne as a Green Beret colonel trying to defend an outpost threatened by the Viet Cong.
An obvious nit is that none of the Viet Cong/North Vietnamese regulars are using the ubiquitous Kalashnikov assault rifle, or for that matter any other Eastern Bloc weapons.
Another gun nit is the "M16" Col. Kirby(Wayne)smashes into a tree near the end of the film. Its very obviously a toy, as the camera gives us a long and clear look at it before Wayne takes his swing.
Amongst the familiar faces are the late David Janssen(The Fugitive, Harry O) as journalist George Beckworth, Star Trek's George Takei as Capt. Nim, and the late Jack Soo(Yamada on Barney Miller)as Col. Cai. None of the main Asian roles are played by anyone of Vietnamese descent, which is not surprising given when the film was made. More annoying is that if you look closely during the attack on the camp you can see that some of the "Viet Cong" aren't Asians at all, but Caucasians.
Don't forget the most glaring nit (and a most famous movie nit), where at the end John Wayne and the little Vietnamese boy watch the sun set in the East!
IIRC, the NVA and VC are largely using the MAT-49 Sub Machine Gun, while the weapons predominently used by these forces would be Russian or Chinese in origin, there would have been a substantial amount of material left by the French forces as evidenced by the Citreon staff car.
MAT49s were common enough that some were converted to 7.62mm Soviet calibre by the Vietnamese.
Which was in itself basically a slight variant on 7.63mm Mauser and already used in the Tokarev TT-33 pistol.
What's Mr. Sulu doing in this film?
(Just kidding)
"An obvious nit is that none of the Viet Cong/North Vietnamese regulars are using the ubiquitous Kalashnikov assault rifle, or for that matter any other Eastern Bloc weapons."
I think another reason this is a nit would be that it somewhat contradicts a scene early in the movie, when some Green Berets explain to reporters why the US is in Vietnam by showing captured Soviet and Chinese-made weapons and Czech-made ammo. It kind of undermines that argument to show the enemy using weapons not made in Communist countries.