Most effective? Possibly not, but if someone already has one (or more), why not use it? I have seen videos of pickups with .50 cal machine guns on the roof- that's usually a one shot kill, but again, not everyone wants one or can buy one. At about a dollar per round (on a good day), it's not a cheap way to do it. Magazine capacity and rate of fire help, but they still need to hit a vital spot.