For some backround: This is the "Security gun rule". Under this regulation, the Social Security Administration will submit information on recipients of disability insurance to the National Instant Criminal Background Check System if they met certain “mental impairment” criteria[0].

As I understand it most of the peopled with disability insurance for mental impairment will be military veterans.

0: http://www.foxnews.com/politics/2017/01/16/gun-rights-groups...