Nothng really exciting, and a lot simpler than a regular impingement rifle.
Gas fills a chamber in what would traditionally be called the gas block, and forces the piston a very short way rearwards, then purges the excess gasses/carbon/etc....the piston then bears against the op rod housing (think of it as a giant carrier key) that rides on a guide rod with a coiled spring on it. (The housing is dove-tailed and screwed to the abbreviated carrier-and the screws are two different lengths, and staked). As the housing and czrrier move rearward, they compress the spring onthe guide rod, and then rebound forward together. The carrier is just shorter than the bolt itself (the bolt head comes out the front, the tail is just inside the back of the carriier).Not much travel (just enough to clear a live round).
I'll see if I can export some of the photos from the manual into this thread at some point this week or next.