You can compare these adjusted numbers to the official NICS numbers.
This adjustment is significant — the NICS numbers are 42.6% higher in 2013 than these adjusted numbers. But the numbers show similar changes in gun ownership over time. The adjusted numbers show a 64.5% surge in gun sales from 2008 to 2013, while the NICS numbers show a 65.9% change.
Yet, there is one reason to believe that these adjusted numbers are too low. Twenty-four states give NICS check exemptions for the 13 million concealed carry permit holders.
Strictly speaking, isn’t the actual rate of blocked purchases under our current background check system less than one percent?
http://www.guns.com/2014/12/09/nics-background-checks-break-200-million/