Printable View
I went shooting with a friend today. He has an AR-15 and I had my axis .223. When we shot the same ammo, the brass that was ejected from his rifle was so hot you couldn't touch it. The brass from my rifle was much cooler. He ask me why this was and I have no idea???
I would imagine your friend was shooting his semi-auto a lot more than you were shooting your bolt gun and thus his barrel got a lot hotter from multiple shots being shot in quick succession. Some of that heat will transfer to the brass making it hotter as well.
I think it's more that the shell casing spends less time in the chamber of a semi-auto. The barrel and bolt act as a heat sink, and the steel's thermal conductivity allows for heat to transfer from the brass faster than it would in air.
88 got it right. If you friend has an adjustable gas block and shut it off so he had to manually eject his brass it would be a lot cooler when it came out of the chamber.
The AR is gas operated, hot gas from combustion causes bolt to cycle.