the Brady bill required those who are allowed to engage in interstate commerce concerning firearms to conduct-through a government agency-background checks to make sure that the people who fill out the federal form 4473 are not lying on some questions that ask if they are "prohibited persons" such as if they are a felon, fugitive, under indictment etc.
Now if the background check determines they are a prohibited person, they have committed federal perjury because if they admit on form 4473 that they are a felon or a fugitive etc, the clerk won't even bother, he will say SORRY you cannot buy a gun.
according to mainly Democratic administrations, this law has "stopped" HUNDREDS OF THOUSANDS OF FELONS FROM BUYING FIREARMS (from licensed dealers). yet in reality, only a few dozen have been prosecuted even though almost everyone DENIED can be charged with perjury. and of course, since few are prosecuted, there is no guarantee that they didn't find another source for firearms
even before the BB, few felons were willing to sign a form and thus committing perjury that would be added on to any other charge that would accrue if they were caught with a firearm. Thus most felons have always obtained firearms from people willing to sell or give them guns which -according to dozens of studies and interviews of felons-mostly involve family members, friends and criminal colleagues. NOT buying guns from private citizens they don't know who well could be informants, feds or state cops and who would be more than willing to testify against them if the cops showed up and said-Hey Dave, you are listed at Joe's Gun shop as having bought a Beretta 92 there on November 1, 2004 and we found this gun on a guy we just charged with felony assault and armed robbery. Now most private citizens will say -Yeah I sold that to him, I had no idea he has a record but I will testify that he did get the gun from me
as opposed to family friends who will claim it was stolen or taken without their knowledge etc