“In sum, gun prevalence is positively associated with overall homicide rates but not systematically related to assault or other types of crime. Together, these results suggest that an increase in gun prevalence causes an intensification of criminal violence—a shift toward greater lethality, and hence greater harm to the community. Of course, gun ownership also confers benefits to the owners and possibly other members of the household. The benefits are associated with the various private uses of guns—gun sports, collecting, protection of self and household against people and varmints. But if our estimates are correct, the net external effects appear to be negative.”Philip J. Cook and Jens Ludwig
The study finds that the social cost for the marginal household gun ranges from $100 to $1800 depending on a number of assumptions.