This study represents an attempt to understand the U.S. firearms market – the largest in the world – in economic terms. A model of the underlying interplay of legal firearms supply and demand is a prerequisite for reliably evaluating the effectiveness of pertinent existing state and federal firearms policies, and to amend them as necessary. The stakes are high: compared to other nation-states, per capita firearms-related harm in the United States (including suicides and homicides) is exceptionally high and, within constitutional strictures, state and federal firearms policymakers increasingly view it as a major and pressing society-wide problem. Virtually all firearms in the U.S. are initially manufactured and sold legally. Solving a simultaneous equation model using the instrumental variable of natural disasters and employing a unique dataset of U.S. firearms prices and quantities, this paper models – we believe for the first time in the literature – the U.S. market supply of, and demand for, firearms. Encouragingly, we find that this market operates as any other would be expected to, with the notable exception that lagged nonmilitary firearms stocks generate new market demand in a positive feedback loop. We test as predictors of market performance federal firearms legislation as instances of policy, as well as of extraterritorial armed conflict, firearms industry concentration, crime, and technology gaps between U.S. and imported firearms. Except for the time-limited Federal Assault Weapons Ban (1994-2004), we find (restrictive) firearms legislation not to influence sales. We also find that acute external violent conflict and certain levels of violent crime, including homicides and mass shootings, drive up unit sales, and that higher industry concentrations in certain submarkets boost quantity supplied, suggesting economies of scale. Taken together, this study’s findings may provide some empirical support for firearms stock reduction programs to reduce the total volumes of civilian arms.