A common mistake, but widely accepted is the 500 Jefferys is a 500 N. E. in a Jefferys double rifle...Same with the 600 N.E. which is also referred to as the 600 Jefferys in some of the few guns that Jefferys built in .600 N.E. I suspect that wordage came out of Africa as the guns were Jefferys in 500 and 600 caliber......