depends on the weapon. an ar15 needs a special trigger/ sear group and you must machine the inside of the lower receiver to accept these parts. this is no "just file this part" thing. first and foremost it is federal crime to convert without being licensed etc.
im not going to say a person shouldnt have full auto but with any weapon as fast as you can pull the trigger then rounds are going down range.
you could be the baddest mofo there is but when you take fists to a gun fight you lose.
This is true.
Different firearms have different ways of doing it, but with the AR, you need some completely different parts. It can be done by someone competent in a machine shop, however.
Its not even worth doing on most weapons, you can be just as deadly, or deadlier with a semi-automatic weapon firing well placed rounds than just spraying and praying.
There is a reason the military went to 3 round bursts on most of its assault rifles - and generally most never have the weapon on anything other than semi.
Edit*
Im impressed delta, you know your shit.