In Oregon, as in most states, a private gun sale requires no background check, paperwork, or questions asked at all (except at gun shows in Oregon). That means ANYONE can purchase a gun: it's just cash-and-carry, no "underground black market" needed. And too many of those sales are to unstable individuals or criminals.
Be safe this Halloween, and demand background checks and other sensible gun regulation to make a new trajectory for our communities away from gun violence.