It's a new gun industry invention: a "NY legal" 50-round five-magazine part for the AR-15 semi-auomatic air cooled rifle. I can't understand how can this be legal in NY or anywhere else*. Just look at the description from The Truth About Guns—you can't miss it:
The concept is solid and well established on Ruger 10/22 magazines: couple a whole bunch of them together at the floorplate and rotate the contraption when the mag runs dry. But FAB Defense took things a step further, gluing five 10-round magazines to a central spoke to create a New York-legal 50-round arrangement. Well, as near as we can tell NY legal...
* Of course, it's for defense, right? Alien zombie invasion defense.