I caught this show last night while flipping around before bed...HOLY BAT BULLETS that looked fun.
When they were testing in the beginning with the first rifle the gas tube was literally glowing cherry red. They recorded the temp with a laser at 725* after a 300rnd dump. Their water cooling design dropped it down unbelievably low for sustained fire. Shorter bursts were holding at around 80* if IRC and longer dumps I think they said the reduction was 40% so I'm guessing what around 200*?