I used to travel by air regularly in the military, and one afternoon, went direct from shooting range training. Only found out later that night I had around a dozen cartridge casings in my pockets, in my boots and floating around my luggage, just from the people next to me on the rifle range.
I knew when the one dropped down my neck though, still burning hot. just was thankful I was to the left of the 20mm cannon, those casings travelled pretty far, plus the recoil was such that one smaller guy moved back 5m after firing 5 rounds with that one.