ORIGINAL: Paul L Mohr
M16's are capable of automatic fire. They are select fire. Used to be semi and full auto. Now some are three round burst, if not all.
As of 2000 (when I left the US army) a majority of the M16's were the M16A2 model which has the 3 round burst and semi-automatic mode. The older M16A1 model had full-auto and semi-auto mode. There were still a few around when I was getting out but they were being phasediout. I'm sure in the deer hunter they used the A1 model. They actually changed the full-auto mode to the3 round burst modebecause they found (in Vietnam) that the average soldier wasted loads of ammo in a fire-fight because they were terrified.