Who are the Prohibited persons?
Another thing that jumped out at me is the category of active records in the NICS database. Of over 7M records of prohibited persons almost 5M of them are for illegal aliens! That's a lot of data and data ain't cheap.
When comparing the table of records to the table of reasons for denia,l posted by Tom above, there is a real disconnect. Compare the high number of denials due to "convicted of a crime" v. the small ratio of records for that category. And denials due to "illegal alien" are really small compared to the large number of records kept.
There has been a lot of talk lately about tracking "adjudicated mentally defective" persons. But there are 1.4M records that only prevented 7879 purchases.
This is very low yield for both "mentally defective" and "illegal aliens" - a really inefficient process. Makes you wonder if there is a better way...