What GAO Found
Investigations and prosecutions.
Federal and selected state law enforcement agencies that process firearm-related background checks through the National Instant Criminal Background Check System (NICS) collectively investigate and prosecute a small percentage of individuals who falsify information on a firearms form (e.g., do not disclose a felony conviction) and are denied a purchase. Federal NICS checks resulted in about 112,000 denied transactions in fiscal year 2017, of which the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) referred about 12,700 to its field divisions for further investigation. U.S. Attorney’s Offices (USAO) had prosecuted 12 of these cases as of June 2018.
At the state level, officials from 10 of 13 selected states said they did not investigate or prosecute firearm denials, some citing competing resource demands and the lack of statutes with which states prosecute as reasons. The remaining 3 states investigated a high proportion of firearms denials. One of the 3 states reported about 1,900 referrals for prosecution in 2017 and about 470 convictions
https://www.gao.gov/assets/700/694290.pdf
There were about 25.6 million NICS checks done in 2017.