That would have me puzzled too, except for what I saw today. I was out at one of the usual places where I go in the desert. Soon after I got there, I heard a strange noise, like shooting, but different. It was coming from just over the next hill, so I kinda' just wandered to where I could see better.
Marvin the Martian!!!! He dropped a coupla' rounds while he was reloading, and I picked 'em up. Same thing. Keep them away from magnetic fields!