There was a nice feature in another train magazine about all the various ore cars produced by the 3-rail train makers. According to the story, K-Line tooled up their own ore car, which is the one being produced by RMT.
BUT when I look at the comparison photos in that article (MTH, Lionel, Atlas, K-Line), I can see no difference between the Atlas (Roco) version and the later K-Line one. I've never had them both in front of me to make a real comparison, but by the photos in that article, they look identical in every aspect (size and detail)... save for the mounting of the trucks. The K-Line ore cars ride high on the trucks.
All the other ore cars have slight detail or size differences: even the Lionel plastic and die-cast ore cars are slightly different.