I suppose one of the advantages of living around a bunch of people that love their guns is that enough of the knowledge has rubbed off on me to the point where I can see through many of their bullshit arguments. One good example is when they try to be cute by pointing out that an AR15 and a M16 aren't the same thing because technically an AR15 is incapable of automatic fire. It'll only shoot once per trigger pull, whereas a M16 can shoot several bullets at once or even empty out the whole magazine. It's an attempt to make the AR15 seem 'tamer' and less 'military.'
The reality is that this is completely irrelevant, and the military will tell you that on rifles like that, semiautomatic (one shot per trigger pull) is the way to go if you actually want to hit and kill people. It allows you to aim more carefully, and if you have a fast trigger finger, you can still get a nice fire rate going. On the other hand, automatic fire throws off your aim and empties the magazine in less than five seconds, so it's a terrible way to rack up a body count. It's meant more for actual machine guns, where the purpose is to fire so many bullets in the general direction of the enemy, that they're forced to hide and can't fire back at you.