TSA fails 20 out of 22 times in tests to detect a loaded guns in airports. One man managed to get a snub nosed 38 through security in his computer bag. However, he is an Iranian businessman - maybe that had something to do with why they didn't check his bag because they had other people to frisk who were more likely to be smuggling something just based on appearances.
http://abcnews.go.com/Blotter/loaded-gun-slips-past-tsa-screeners/story?id=12412458