Hot and cold

[Bat Rastard]

So I am at the range and I noticed something.

Brass from my AR is Hot!
Brass in my 30BR is cool to the touch.

Is there a simple explanation?

 

[Intell]

Gas operated possibly?

 

[WSnyder]

AR brass is hot because it’s ejected immediately after firing and still retains the heat from firing. BR (assuming bolt action) sits in the chamber for a moment and the heat sink/barrel draws the heat from the brass before it’s ejected.