Envy just downed Ragnaros on Auchindoun. I believe it was done on ten man but not sure. The realm first looked too only be 10 players. Will probably update soon on wowprogress.
Envy guild feed: http://eu.battle.net/wow/en/guild/auchindoun/Envy/
Edit: It is 25 man, I only got 10 achievements popping up in chat. But after checking their distributed loot I quickly saw several names that didn't pop up with achievement. So world 3rd 25 man HC ragnaros it is.
Killshot: http://img51.imageshack.us/img51/648/wowscrnshot072811213122.jpg
http://img94.imageshack.us/img94/730...2811212949.jpg