Bureau of Justice Statistics Bulletin: Background Checks for Firearm Transfers, 2005 [open pdf - 308KB]
"In 2005 about 8.3 million applications for firearm transfers or permits were subject to background checks under the Brady Act and similar State laws. This is an increase of 2.4% from the 8.1 million applications in 2004. The FBI processed nearly 5.0 million of these applications (60%), and State and local agencies processed 3.3 million (40%)."
Bureau of Justice Statistics: http://www.ojp.usdoj.gov/bjs/