"In 2015, nearly 17 million applications were subject to background checks, and about 226,000 (1.4%) were denied, including about 107,000 denied by the FBI and about 119,000 denied by state and local agencies. Nearly 197 million applications for firearm transfers or permits have been subject to background checks since the effective date of the Brady Handgun Violence Prevention Act (Brady Act) on February 28, 1994, through December 31, 2015. During this period, more than 3 million applications (1.5%) were denied. Data in this report were obtained from the Bureau of Justice Statistics' (BJS) Firearm Inquiry Statistics (FIST) program. Through FIST, BJS obtains background check information on applications and denials from state and local checking agencies and combines it with the FBI's National Instant Criminal Background Check System (NICS) transaction data to produce an estimated number of background checks for firearm transfers or permits since the effective date of the Brady Act. [...] These statistical tables describe background check activities that occurred in 2015. Data include the number of firearm transaction applications processed by the FBI and by state and local agencies; the number of applications denied and reasons for denials; estimates of applications by jurisdiction and by each type of approval system; and FBI denials referred to the ATF DENI Branch."
United States Bureau of Justice Statistics: https://www.bjs.gov/