3. Actors

Approximately 40% of annual gun crime in the US is perpetrated with a weapon obtained through a Straw Purchase or the Gun Show Loophole. The University of Chicago recently published a report showing that only 3% of polled inmates incarcerated for a gun crime owned a weapon that they bought through a Federally licensed gun store. 

Whether people who sell weapons in this roundabout way do it for the sake of convenience, or because they believe that background checks are infringing on their rights, they are directly contributing to a significant portion of gun crime in the US.