Huh, so here I've been saving my spent casings in the hope of selling them on eBay, yet for some reason they're banned there. Don't know why, because you can buy other gun parts there, and even inert rounds on there, and brass is literally just brass.
evilBay is very weird about what they allow when it comes to guns. Some gun parts are okay, some aren't. Spent brass is just...brass, though, so I don't know why they would have a problem with it.
My guess is that they're concerned live ammunition might get bundled with the empty brass, subjecting them to liabilities.
I had the same thought. Also, some guy buys spent brass from evilBay, reloads it, uses it to murder someone, then the victim's family sues evilBay for selling him the "bullets".
I suspect the spent gun powder might set off some of the bomb detecting equipment used on some air mail which goes through commercial airports.