Depends on your skill for effective range. I have hit man sized targets at 750 meters with an M16, but that is beyond what is considered the max effective range. In some states it is not legal for deer, in others it is- my personal opinion- too light for deer.
BTW, if you want to buy an M16, you need to be 21, live in a state that permits it, pay a $200 transfer tax, and have a heavy duty checkbook. A legal, transferrable M16 is about $22,000 right now. No, all those zeros were NOT a mistake.
What we have heah is.... failure to communicate.