Multiple shot weapons are guns or rifles that fire more than one round without reloading. The second amendment was adopted in the time of single shot firearms. It is not possible to commit mass murder with a single shot weapon. After firing each round, the shooter is effectively unarmed for several seconds while reloading - time in which others are able to subdue him. This is undoubtedly what the framers envisioned.
Individuals should not have the power of life and death over dozens of others. The right to bear arms does not extend to private ownership of fully automatic weapons, it should not extend to multiple shot weapons for the same reason - the cost to society far exceeds any benefit. History proves we cannot keep them from crazed hands.