@chaplainDMK: The M16 is manufactured specifically for military use. Again, it is important to recognize and distinguish between M16s and civilian rifles when you talk about legality of purchase and ownership.
Explain the difference apart from designation.
There are differences in the trigger, bolt carrier, etc.. The M-16 is select fire, while a civilian AR is semi-auto. The M-16 is built and distributed to military, while civilian ARs are not. Those are a few differences.