How about some more fun with numbers?
There are about 800 Million airline passengers per year in this nation. We might take a conservative estimate that 5% of the US adult population now has permits to carry or otherwise legally carries on a regular basis. That works out to 800,000,000 * .05 = 40,000,000 annual airline passengers likely to be carrying a gun on a regular basis.
40,000 guns carried onto planes each year out of 40,000,000 passengers with permits works out to 1 out of every 1,000 passengers who likely has a gun making the mistake of forgetting he has that gun as he walks through a TSA security checkpoint.
Of course, the better TSA claims to do at intercepting guns, the better the numbers look for law-abiding gun owners. If TSA's success rate on guns is closer to 50%, that means only 4,000 guns were carried through security (with 2,000 being detected) and that means that only about 1 out of every 10,000 gun carrying passengers made a mistake.
I wonder how these numbers compare to passengers forgetting bottled water, toiletries over the TSA size limits, pocket knives, etc. If I recall, 9/11 didn't involve any guns at all, but only relatively small--and then perfectly legal/permissible--knives/box-openers. Imagine if everyone who forgot a small knife or pair of scissors was treated like the small number of persons who get caught with a gun.
Furthermore, don't recall any news about anyone trying to hijack a plane with a gun recently. So unless TSA magically managed to only detect those guns that were being carried on with ill intent, while missing the guns carried on without any malicious motives, we might observe that somewhere between 2,000 and 38,000 guns were carried in the cabins of commercial airliners by private citizens and none of these guns were used to any ill effect, none of the guns went nuts and shot up the airplane by themselves, nothing bad happened.
Finally, from personal experience, the poor performance of TSA to detect weapons is not surprising. Several years back I lost a small knife. Then, a couple of years I go I was traveling weekly for several months. On about my 20th flight (10th round-trip), TSA saw something in my carry on backpack. They scanned it a second time, took stuff out, then x-rayed it a third time. They finally found my lost knife in the bottom of one of the inside pockets. I decided that if I hadn't used the knife in the previous couple of years, it probably wasn't worth it to pay to mail it home to myself so I just surrendered it. Now, admittedly the knife was very small. But TSA missed it some 19 times before they found it on the 20th time.
TSA, like the IRS, BATFE, and some other multi-letter agencies are the epitome of government power run amok and infringing our liberties while not even making a half-way decent delivery on the promise of increased safety.