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.