You are in far more danger from your government than you are a mass shooter.
Governments, primarily “redistributionist” governments, murdered at least 169,000,000 of their own citizens in the 20th century alone, and depriving those citizens of the means of defending themselves was always the first step.
http://www.hawaii.edu/powerkills/NOTE1.HTM
Democide is one of the top killers in the last 100 years!