Muscles,
Like others have said, it's harder to set them off than you may think. I used to have the same fears though. Since then though I've dropped live rounds on hard surfaces (inadvertantly, mind you), pushed like h*ll to get them into magazines, taken live rounds apart, etc. I'm convinced that they are pretty stable...not sure on the high heat issue though.
Once I was messing around with a round I had taken apart, because the case had been severely damaged by a misfeed. I had removed the bullet and the powder, and, out of curiousity, I wanted to set the primer off. I stabilized the case, primer up, on concrete, placed the tip of a Phillips head screwdriver on the primer, and whacked it with a hammer. It took several tries before I scored the necessary direct hit with sufficient pressure to set the primer off. Even with several small dents from failed hits, the primer didn't go off.
Also, at least with all the rounds I've ever worked with, the powder isn't compressed in the case...it's loose, with at least some space between the bullet base and the powder, assuming a case sitting with the bullet end upwards. Take a round in your hand sometime, put it up to your ear and shake it. You'll probably be able to hear the powder moving. Until I first took a round apart, I used to think the powder was stuffed in there tight, and that it would be pressure-sensitive. That's not the case, at least, like I said, with all the types of ammo I've ever used.
Hope this helps reassure you a bit.
[This message has been edited by BAB (edited November 17, 1999).]