If high capacity magazines aren't helpful for mass killings, why are they used in those killings?

[HooptieWagon]

11. The increased rate of fire comes with a decrease in accuracy.

Firing wildly into a crowd will no question kill and wound many. However, it is inefficient. Once a person is dead, putting extra bullets into the body is wastefull (although the gunfire itself creates terror). And of course bullets that go wild neither kill or wound. Ammunition is a concern because it costs money, but more important it's heavy. If these were experienced shooters (say with military experience) they likely would use a combination of pump-action shotgun (possibly sawed-off barrel), and a couple of handguns with a few extra magazines. Then a little time to aim more carefully and make the shots count. In some cases, like Aurora, it would have doubled the casualties. In Sandy Hook, likely little difference...the inability of the shooter to get in the classrooms that were locked prevented greater casualties.