Some powders are more heat sensative than others, along with the fact that some powders can change property when vibrated enough, that's why you're not suppose to put loaded ammo. through a tumbler.

Just because Mythbusters can't replicate something certainly doesn't convince me that it can't happen. They couldn't even get a robbin hood with arrows!

Just like the guy that I posted about earlier that had handgun ammo. on his dash, isn't it strange that not all the ammo. went off, but instead only 2 rounds of the box of 50. He also posted pictures of that incident. SO, no doubt it CAN happen.