Got it on my second try. As stated above, do it on easy and reload your gun during the brief breaks in the action. They almost always occur while moving from one mini hot zone to the next. Auto lock onto each target hit them once and move on. Even if you miss 2 or 3 targets you can still get this achievement with relative ease.
If you're having trouble hitting anything during the dual wielding segment just make sure you put the cross hairs over them and squeeze both triggers simultaneously. Pace your shots to keep the reticule a manageable size in the same manner you would if you were shooting a single gun from the hip. This will maximize your chance of getting a hit (you only need one hit to kill on easy). Good luck!