End Purchase of Firearms by Dangerous Individuals Act of 2017 This bill requires each state to: establish a reporting system through which mental health professionals may report information about an individual committed to a mental institution who poses a danger or an individual who communicates a serious threat of violence, provide mental health records to the National Instant Criminal History Background Check System for use in determining whether a person is disqualified from possessing or receiving a firearm, and establish a process related to the temporary involuntary commitment of individuals at mental health facilities. Beginning 10 years after enactment, the Department of Justice must reduce by 5% funds under the Edward Byrne Memorial Justice Assistance Grant Program for a state that fails to comply with requirements. The bill amends the federal criminal code to expand the categories of prohibited persons (i.e., persons barred from receiving or possessing a firearm) to include persons who communicate a serious threat of violence to a mental health professional. Finally, it replaces various statutory references to persons adjudicated as a "mental defective" with persons adjudicated as "ineligible due to disqualifying mental status."