A society can limit massacre death tolls by regulating gun design features.

Evidence

However, it is within a society’s power to limit the extent of the human toll a killing spree exacts. This is tellingly revealed in cases where the death toll was cut because the gunman’s semiautomatic weapon jammed (Johnson & Kovaleski, 2012). Society can exercise some measure of control over the scope of massacres by limiting two features of gun design: banning semiautomatic, military-style rifles and restricting the bullet capacity of magazines. — Albert Bandura, Moral Disengagement, 1334