Isn't that the rifle that Al Pacino used at the end of Scarface when all of the Columbians attack his house? That's only reason you need one if your a drug lord and you have a whole army of assains trying to kill you. But that's just my opinion.
movies dont = reality.
and pacinos charecter used an M16. while the operation is similar ( think recipricating internal combustion Vs other) but it was automatic, and hence restricected by the 1934 NFA bill and the 1986 MG ban. an AR15 is a semi auto only version that would require exstensive work to make F/A ( think Yaris Vs Porsche)