The HKs are in fact not gas operated. They are recoil operated.
The flutes cut in the chamber are there to keep the case walls from sticking to the chamber.
Better tell Wikipedia that they have it all wrong then;
(from Wikipedia)///// The HK416 is an assault rifle designed and manufactured by Heckler & Koch. It is a modified version of the American M4 carbine with many changes, most notably a new gas operating system from the Heckler & Koch G36\\\\\
Wha?