I don't think that's how ammo goes off.......in a fire, without the compression of the barrel and bolt, self-contained cartridges will "pop" splitting open the case and not having any meaningful velocity.
I could test this but with ammo prices so high right now, I'm just not going to do that.
Oops! Replied before seeing the excellent video above. Looks like it's been very well covered already.
*I had this same discussion with a firefighter that I met while staying in a Vermont motel. He shook his head a few times then (to his credit) admitted his station chief had told him wrong!