None.
There are something like 300 million guns in private hands in the USA, and about 99.99999% of them will never kill anyone or be used in a crime. More people are killed with hammers than with the so-called "assault rifles" that everyone wants to ban.
To this post, again, I disagree with you. According to "you", 99.99999% will never kill anyone, yet, every year, over 19000 american gun owners kill themselves with guns. Over 11,000 americans will die at the hands of a gun owner every year.
According you you, less than 1/10th of 1 percent are the evil gun owners, yet the numbers dont match up.
We will never know what percentage of gun owners suffer from mental disorders or psychological disorders like depression or alcoholism. To that end, we will never know who should or shouldnt be armed.
Until this country tests for mental illness or past behaviors that include drunken behaviors or depression, then every year, nuts with guns will commit horriffic mass shootings.
99.99999% is a rather over confident view of gun owners.
For me, if i had to put a number on it, I'd say that close to 25% of total gun owners shouldnt be allowed to own guns for some disqualifying reason.
TOS.