From the National Shooting Sports Foundation:
The November 2018 NSSF-adjusted National Instant Criminal Background Check System (NICS) figure of 1,314,193 is a decrease of 9.8 percent compared to the November 2017 NSSF-adjusted NICS figure of 1,457,103. For comparison, the unadjusted November 2018 FBI NICS figure of 2,363,705 reflects a 0.4 percent decrease from the unadjusted FBI NICS figure of 2,372,888 in November 2017.
The adjusted NICS data were derived by subtracting out NICS purpose code permit checks and permit rechecks used by states for CCW permit application checks as well as checks on active CCW permit databases. NSSF started subtracting permit rechecks in February 2016.
Though not a direct correlation to firearms sales, the NSSF-adjusted NICS data provide an additional picture of current market conditions. In addition to other purposes, NICS is used to check transactions for sales or transfers of new or used firearms. FBI NICS and NSSF-adjusted NICS figures do not account for firearm sales or transfers using approved alternate permits such as a concealed carry license. Several states allow the use of such alternate permits that have become popular among consumers over the past several years.
It should be noted that these statistics represent the number of firearm background checks initiated through the NICS. They do not represent the number of firearms sold or sales dollars. Based on varying state laws, local market conditions and purchase scenarios, a one-to-one correlation cannot be made between a firearm background check and a firearm sale.