Rand said this on Hannity. I will post the interview when I get it.
He said there were 40 prosecutions last year from failed background checks. Out of 14,000.
John Lott, the pro-gun scholar, has often cited this statistic.
The reason there are so few prosecutions is the prevalence of "false positives" -- background checks submitted with mistakes in them or that were misread. Something over 90% of them pass muster if they're re-submitted with complete and correct data.