Bergen
Where did the photo come from?
I have checked all of my books and it appears that no one produced a 2" .600 cartridge My view is that some one was just messing with it for their own enjoyment or they were messing with our minds
Now is you have a look at the cartridge on the left of the little 600. I cannot find any reference to a 3 1/2 inch 577 in any book that I own.

British sporting rifle cartridges. Bill Flemming
Eley Cartridges .Harding
Kynoch. Hedlund
Cartridges of the World
Birmingham cartridge manufacturers . Harding
and the list goes on.
Whoever put the photo together didn't do their research.
all the best