During the Vietnam War the M16 rifle had a reputation of being unreliable. There are stories of US personnel discarding their issued rifle and instead using captured AK-47's. How true are these stories and how widespread was the practice?

Early M-16s arrived in Vietnam with the mistaken understanding that they were a space-age advanced weapon that did not have to be cleaned and therefore seldom included a cleaning kit. Like any rifle, however, regular maintenance is necessary and once cleaning kits and a comic book full of instructions (yes, an actual comic book) were provided the weapon began to receive rave reviews. Soldiers struggled with the weight of its predecessor, the M-14, and could not carry as much ammunition or fire the weapon accurately on full automatic. The M-16 gained a reputation for its accuracy and lightness (5 pounds versus the 9 pound M-14) and further versions only improved the rifle. Soldiers still complained that the M-16 lacked "stopping power" and that due to ambushes where they couldn't see the enemy the usual 200 rounds were insufficient for patrols. Many soldiers carried as much as 500-600 rounds for this reason. Captured AK-47s were rarely used by US personnel because their distinctive sound and the different tracer ammunition color meant that they risked friendly fire if they used captured NVA/VC rifles. A great introduction to US experiences in Vietnam is Eric M Bergurud's book Red Thunder, Tropic Lightning.