Yes very different, same name 2 different continents. I don't know why when I saw the question, I automatically thought of Rocky Gibbs.(embarrassing!)
Now John, to answer your question correctly. The .256 Magnum was designed by Gibbs Rifle Company in 1913 and pretty much duplicates the 6.5x55 in both case capacity and performance.

Now I will slink away and hide under my rock.