Yeah, M-16's I guess were notoriously bad in Vietnam. I'm not a gun nut, but here's what I found.
"Everything went wrong with the M-16. For one, Colt didn't have a quality control system set up at their factory. A large percent of the barrels Colt was manufacturing were faulty when they were first fired.
The narrowness of the barrel increased the amount of moisture that would enter the barrel and chamber.
Different batches of WC846 had different amounts of calcium carbonate which would foul barrels, and that was probably exacerbated both by the conditions in vietnam and the military's insistence that that the M-16 didn't need maintenance, which, partly was because of how the M-16 was procured and the environment it was procured in, it was first adopted by air force special forces without the normal trials, and the army was planning on adopting the SPIW weapon, so they viewed the M-16 as a stopgap and didn't want to spend money on cleaning supplies or training, and the cleaning supplies (the lubricant) was unsuited to the M-16. The chamber and the barrel iirc weren't chromed, they were using a huge amount of tracer ammunition and that probably contributed to things.
A million different things went wrong."
