In the 90s I was jumped on by security at Detroit Airport. I had bought a small box of a 100 bullets, for a friend, of a caliber that was rarely available in germany. I had put these in my handluggage because they were heavy metal. When I got angry of being jumped on, and abused by the lady that had given me the vocal security talk down before, for these metal-pebbles, a young officer tried to calm me down. He had been trained with those old "SF improvised munitions handbooks" and told me, that somebody else could bring in the empty shells, another one the powder, another one the caps, another one a steeltube, another one the screwd on tubecap, another one the wooden frame-handle and another one the rubberband and nail and they could assemble and load this all in the toilet. In all my life I have never heard of a plane being hitchhiked with such an item, but these people are trained to believe this.