Not only do they get hot as hell they have a certain smell to them.

I was shooting my suppressed AR in a light rain and it didn't take very long for the rain drops to start sizzling and cooking off from the can.

Back in Basic, we were doing a night fire exercise from concrete dugouts. My battle-buddy's AR jammed (Vietnam-era POS), and the Drill took all of his mags and moved them to my side of the berm. He instructed me to be sure there was no ammo by the time the flares quit.

These were A1 variants, so I flipped to full auto and began mag dumping. I don't know how many I went through, but when the flares quit and the dugout went dark, the barrel was glowing white under the hand guards out to the gas port. Good times. I would never treat my ARs that way, but I don't have a drill sergeant threatening me while I'm out shooting my own stuff.