By the end of 2010, prosecutors had only 32 convictions or pleas agreements, and only 13 of those involved falsified information when buying a gun or illegal possession of a gun, that translates into just 0.018% of the 71,010 initial denials.
…
These numbers are just one of the reason that no study by criminologists or economists has found that the Federal Brady Law has reduced national crime rates.

Of course, being falsely labeled as being ineligible to own a gun isn’t the only cost imposed on law-abiding Americans. Even those who aren’t prevented from buying a gun face delays in getting approved.

John Lott
June 13, 2011
The Problem with Brady Background Checks: Virtually all of those denied purchasing a gun are false positives
[Via David Hardy.

When advocates of background checks crow about the Brady checks stopping millions of gun sales realize they are celebrating the delay and/or denial of a specific enumerated right.–Joe]