I recently carried 5 rounds of .38 Special ammo through two security checkpoints.
I have a nice carry on bag that my girlfriend gave me which I use on trips. She and I took a weekend trip to San Antonio. She was driving, so I put my J farme in the side pocket inside the bag. When we got back from the trip, I spent the night at her place, and her young son was there with us. I unloaded the gun, left the rounds in the bag and put the gun in my car.
The rounds stayed in that bag for 3 months until my trip to Vegas. The J frame isn't in my normal carry rotation, but I like taking it on car trips for whatever reason. The side pocket is hardly ever used, and the rounds were not noticed by me when I packed.
I made it through security in Houston (IAH) without incident. At the Vegas airport, the TSA agents pulled my bag off the scanner and asked if it was mine. I actually thought that they were investigating the cash that I had in the bag (imagine that, leaving Vegas WITH cash for once). They ran it through the scanner again, and then called a supervisor. I was getting a bit irritated that they would ask about cash in my bag on a domestic flight as I had experienced a few run ins of this type before.
The supervisor then said something that made my blood run cold - "Sir, do you own a gun?" Thoughts of the San Antonio trip raced through my mind, including the memory of me placing my revolver in the bag. I responded affirmatively, and then she said that there looked to be 3 or 4 "bullets" in the bag. I instantly flashed back to unloading the revolver and then to placing it back in my safe at home. Relief rushed through my body at the fact that at least I hadn't packed the actual gun. I told her that there were probably 5 rounds from my revolver that I had forgotten. She hand searched the luggage, confiscated the rounds and let me go on my way.