Okay, one last thought. Maybe it has something to do with the difference in the burn rates and heat of explosion characteristics of the different powders involved?
50 BMG powders are some of the slowest in the world. On the other hand, .223 are some very fast powders. Everything else is a gradual slowing down to 50 BMG. Seems to me like maybe faster, hotter powders would glow hotter and like a torch turned way up and the brass is unable to dissipate the heat generated fast enough from that instanateous burst of energy so that it is cool to the touch. On the other hand, 50 BMG is burning tar that takes longer to burn but maybe doesn't burn as hot and maybe the brass can dissipate the heat about as fast as it gets transferred from the explosion? But longer slower burn is more gentle on the brass,
and more gentle on your hand. That is the only explanation I can think of that makes sense to me.
There has to be some correlation of absolute mass of powder per unit of volume that compensates to some extent for the
.50 cal shell size vs. its higher powder charge so that its a ratio thing. It can't be the whole answer to me. So, I'm guessing the only other difference is the type and burn rate and energy release rate of the powders themselves?? Maybe I'm groping in the dark
but it makes some sense to me.
We need a lab to run this skin burn test under controlled conditions......who wants to hold on to the brass from each test??