Other mistake: In the scene where Mel Gibson fires off a few rounds into the nearby woods and bushes to see if there are any NVAs, there is a M60 crew, the weird thing about them is that you can only see the muzzle flame from the M60 the first couple of rounds - after that there is no muzzle flame, but the M60 continues to fire at the same rate.
Other mistake: When the black guy from their base gets shot in the head the camera slows down and you can see his forehead starts bleeding but there's no hole on his helmet. [Actually there is. If you pause it, you can see it on the (his) right side of his helmet. Although it looks as if it exploded outwards instead of inwards as a bullethole would.]
Chosen answer: There is no definitive information on this topic, and although factually accurate, a technical problem with a weapon was probably not enough to build an entire sub-plot, and would not hold the interest of the moviegoer. There were enough casualties without having to take into consideration weapon malfunction.
Macalou