"George Burke, a spokesman for Democratic Rep. Carolyn McCarthy ... of New York, said millions of criminal and mental-health records are not accessible to the National Instant Criminal Background Check System, mostly because state and local governments lack the money to submit the records." (from cayote33's posted source)
Just how many of those millions of people, representing by those millions of records, should be disqualified from having guns?
"People who cannot contain their urges to harm (or kill) people repeatedly for no apparent reason are assumed to suffer from some mental illness. However, they may be more cruel than crazy, they may be choosing not to control their urges, they know right from wrong, they know exactly what they're doing, and they are definitely NOT insane, at least according to the consensus of most scholars (Samenow 2004 [
http://members.cox.net/samenow/)]. In such cases, they usually fall into one of three types that are typically considered aggravating circumstances in addition to their legal guilt -- antisocial personality disorder (APD), sociopath, or psychopath -- none of which are the same as insanity or psychosis. APD is the most common type, afflicting about 4% of the general population. Sociopaths are the second most common type, with the American Psychiatric Association estimating that 3% of all males in our society are sociopaths and Stout (2005) estimating 4% of the population. Psychopaths are rare, found in perhaps 1% of the population...the field of criminology tends to treat APD as so synonymous, in fact, with criminal behavior that practically all convicted criminals (65-75%) have it, with criminologists often referring to it as a "wastebasket" category."
http://faculty.ncwc.edu/toconnor/428/428lect16.htm
There you have it - 1-4% of the US population (3-12 million) might be denied guns. While only about 1% of the US population have CCW permits, a much larger percentage have guns - so we can't confuse CCW with the opportunity to buy/possess/use guns.
Of course, the experts will probably say that the desire for guns probably qualifies one as disqualified to have guns ... Catch 22.