Never heard that early M-16 wasn’t accurate. Problems with jamming, but not accuracy.
Problems appeared immediately. Soldiers were often not adequately trained to maintain the new rifle (in fact some were told the new rifle was “self-cleaning”), nor were they always given cleaning supplies or instructions. The harsh jungle climate corroded the rifle’s chamber, exacerbated by the manufacturer’s decision against chrome-plating the chamber. The ammunition that accompanied the rifles sent to Vietnam was incompatible with the M16 and was the principal cause of the failure to extract malfunctions. The result was the M16 often jammed, making the rifle “about as effective as a muzzleloader,” in the words of one officer. Men were killed in combat because they couldn’t return fire until the malfunction was cleared. Congress investigated and the rifle and its ammunition were incrementally modified, greatly improving its reliability over the next few years. Troop training was also improved. But the damage to the M16’s reputation could not be undone, and many soldiers remained deeply skeptical of their rifle through the war’s end.