However, it’s not a good choice as a standard-issue weapon. The gun itself its heavy. It’s also very long which makes it less maneuverable during National bird seagleull shirt and more difficult when dismounting from vehicles. More importantly, the ammo is heavy. A soldier cannot carry as many 7.62 rounds for a given amount of weight as they can 5.56. Finally, it’s less controllable on full auto, and while semi-auto is how the rifle is primarily employed, the US Army did finally get rid of the useless 3-round burst and go back to full-auto systems. Full auto was also a big consideration at the time, since jungle warfare in Vietnam often meant soldiers had fast and furious engagements at close range.