The purpose of the present study is to determine the effects of federal and state assault weapons bans on public mass shootings. Using a Poisson effect model and data for the period 1982 to 2011, it was found that both state and federal assault weapons bans have statistically significant and negative effects on mass shooting fatalities but that only the federal assault weapons ban had a negative effect on mass shooting injuries. This study is one of the first studies that looks solely at the effects of assault weapons bans on public mass shootings.