lol the article you cited proves that they do not succeed due to the fbi not doing their job! the fbi failed twice in his case. they have 3 days but... "The FBI also has up to three months to complete the background check after the three days expire. Federal agents can confiscate a gun if it turns out someone should not have been allowed to buy it."
and... "A few months later, he shot and killed nine people"
the fbi should have confiscated the gun.
this is a failure to enforce laws already on the books. roof didnt sneak a purchase through a gun show he went and bought it legally and the fbi failed to confiscate it! the article says 3.59 percent of 8.6million sales did not complete a background check in 3 days. thats 308740 sales without a background check within 3 days and you have proof of 1 person.
also the article you posted linked to this article: www.nytimes.com/interactive/2015/10/03/us/how-mass-shooters-got-their-guns.html
showing that background checks did/would not have prevented the killings.
even if the background checks stoplrd them, do you honestly think that these people so intent on killing would not have been able to obtain firearms by other means?