That is not what you said.
A denial is not the same thing as preventing a sale to a criminal. They even have an appeals process for people who are denied and believe that there was a mistake. Funny thing about that, since any finding of a proceed has to be cleared within 24 hours it is entirely possible for someone to get denied, file an appeal, win, and still get denied the next time they buy a gun. That is why they set up the VAF system where you can elect to keep your records on file so that, when you get denied, they can see that they are wrong. Despite this, they still managed to deny people in that system 4,020 times in 2012 alone.
FBI ? NICS Operations Report 2012
In case you have as much trouble with math now as you did last time I showed you some numbers, that is roughly 5% of the denials they had for that year. That figure is only a small portion of the number of appeals they receive each year.
Tell me something, oh font of all things stupid, if they actually catch over 38,000 criminals trying to buy a gun every year, which is a ******* felony, why aren't they arresting them?