Spent brass in mine, too -- which actually went inside my backpack. Went through airport security (this happened last year in Atlanta Hartsfield) and got detained and questioned for an hour. The screener called his supervisor who called his supervisor who called the head supervisor. Three supervisors. I guess they've never encountered anyone with a spent brass in their belongings before. I had to explain I went shooting the day before and luckily had my range membership card. They had to verify and call the range. They asked a million questions to determine my identity and why I was leaving the country (I was headed to visit family in Canada.) What an inconvenience if anything else. But I'm glad they were vigilant about these things to ensure everyone's safety.
Oh and the worse part-- as soon as the head supervisor approached me, the airport police stationed on a podium platform in the middle of the floor issued an "EVERYBODY FREEZE, DON'T MOVE" command to the entire airport security check-in area. We were all instructed to freeze over a loud speaker. You could hear a pin drop. It was so scary. To this day, I still don't know if that command was directed because of me.