These are useless laws with regard to public safety and I strongly suspect Ferguson knows that to be the case.  To "justify" such laws, one must concoct categories like "Assault Weapon" and "Mass Shooting".   An assault rifle is a selective-fire rifle that uses an intermediate cartridge and a detachable magazine.   It is a weapon used by the military and is generally not available for sale in the US at all. The term “assault weapon” was made up to describe weapons that look like an assault rifle but work quite differently (semi-automatic only).  One could call all smooth coated dogs  “pit bull dogs” and it would be similarly honest.  There is NO actual definition of “mass shooting”.  It is copied from the FBI defined term “mass murder”, but can be anything you want to call a mass shooting.  Even using these two fake terms, it appears there has only been one case like this in the last 20 years: http://www.seattletimes.com/seattle-news/crime/mass-shootings-in-washington-state/