Many moons ago, in the grip of an Alaskan winter, my mother decided to 'burn' some trash in our fireplace to get some wood started. Not knowing a couple of Air Force issued 45 shells had fallen into a bedroom trash can (spilled off the dresser?) she and my sister snuggled up to the warmth only to be rudely awakened by a couple of blasts.
Ashes-on-fire were quickly upon them. My question is: how lethal might the projectile have been, given that the casing was probably moving with the same speed in the opposite direction? [True Story]
From what I've read, ammunition which is not contained in a firearm barrel isn't much of a threat. As soon as the powder starts to burn, the seal between the casing and the bullet will be opened, allowing most of the gas to escape harmlessly. In an experiment where rounds were placed on a metal table which was heated until they cooked off, casings usually travelled less than a foot. In some cases, the bullet stayed attached to the casing and the primer went flying (after which all other gasses vented out the primer hole). The primer could fly some distance, but because of its light weight wouldn't pose much of a threat.