One thing to take away from this is with direct-impingement systems, the gas vents out the bolt carrier almost completely before the bolt unlocks. There is some residual gas in the system that gets into the action, obviously, but on a properly-gassed system, it’s nowhere near as dirty as some AR haters would like to think.
And if you liked that, check out Episode 2: Sniper. This quality of slow-motion video these guys are getting is just phenomenal. For the camera junkies, they used a Phantom Flex to shoot these.