The stockpile of handguns, rifles and magazines were discovered during a search of Deron Harris' apartment in Morton.
Police say the search was prompted by an encounter in Prospect Park Wednesday morning.
The 40-year-old allegedly fired a gun into a car occupied by his ex-girlfriend and another man.
Harris faces attempted murder for that shooting incident, along with a slew of other charges related to the weapons.
Police say the seizure likely saved lives.