i can speak with a little personal experience as far as ammo & fire. i had a detached garage that burned to the ground two years ago. it was a HOT fire too. in one of the hot spots, i had 3 50 cal ammo cans on a shelf. one was 820 rds of 5.56 green tip, the others were 240 rds of greek m-2 ball 30.06 from the CMP. there was also a 500 rd case of barnaul 7.62x39 in cardboard. the 7.62x39 started first & ended up scattering about 1/2 of them onto the floor, where they survived at the cooler temp level. a couple of the rounds that went off punctured one of the cans of 30.06, allowing it to get hot enough inside to ignite 64 rounds.the rest of the ammo in that can, although needing some cleanup, shoot fine. the ammo in the other two cans survived without a scratch. the cans warped up pretty bad & the seals melted, but inside contents were protected.
best advice i can give is store all ammo in mil-spec cans & keep them low on the floor if possible where temps wont be as high. thats how i have all of my ammo stored now.
here are a couple pics of the can that was punctured & the leftovers of the 64 rds that ignited.