I guess EBay is slipping up. They allowed a firearm receiver to be sold without an FFL. I thought that violated their rules. They probably didn't realize it was a firearm receiver.
The receiver rail certainly seems to have a depression just behind the chamber area. The way the light is shinning on the rail, it is difficult to tell if it is in fact a slight depression. A good straight edge would tell if the rail is depressed in that area.
