It is a misleading statistic, and likely not empirically based. The relevant statistic would be "x% of NEW
firearms are sold without a background check". But the percentage would be virtually zero, so that number isn't much help to the gun control crowd. They conveniently talk in terms of closing the "gun show loophole" when they are really pushing for a federal ban on unregulated private transfers of firearms within a state
I just heard this morning that the big regional gun show in Ohio (Bill Goodmans) is now requiring ALL of their table/booth vendors to run background checks. From their website:
All Firearms sold, traded, transferred or disposed of by FFL Table holders must undergo background checks as per Federal Law (No Exceptions). Non-Licensed Vendors (Private Sellers-Collectors) hereby represent that they will voluntarily agree to have background checks performed on all firearms sold at the show thru "House FFL's". (A $50 "reward" will be provided to anyone, whether a vendor or attendee, who reports a substantiated violation of any vendor's commitment to perform background checks on any firearm sale.) All vendors who have any firearms for sale must display a "Background Checks Required" signage provided by promoter.
So, they voluntarily closed the so-called gun show loophole. But that isn't really what the Brady folks are talking about. They don't like that most states don't buy into their nonsense, and choose to regulate the commerce within their borders as they see fit.