When america was developing the bombs that they were going to drop on Nagasaki and Hiroshima they had 3 cores of plutonium called the Trinity core, the Fat Man core, and the Demon Core. In order to transport these cores they developed this case out of magnesium. I discovered this case while watching this:

https://www.youtube.com/watch?v=aFlromB6SnU

Super interesting mini-documentary that I recommend you watch because its both cool and terrifying.

The replica I made is 1/4 scale to the original and the interior has been changed (I assume, There is no declassified sources I could find showing the interior) to be as large as possible. 

Originally it was made for personal use so it might be a bit janky in places (holes requiring sanding and such.)