I have posted this on another board, but did not get anymore information then I already knew, Maybe someone here can help.

I have not seen the double and this was the information that I was given. I have checked a couple of books I have and understand that the Lancaster with oval barrels and a gain twist was manufactured up until the late 1920's. However no examples of calibres and/or cartridges was given so I am at a loss myself. By the way, these rifles were both nitro and blacpowder proffed I guess as per the customers preferrances

From Steve Meyer(Thanks Steve):

Neither can I find any reference to a .480 Lancaster in Hoyem, Fleming or any other book I've seen. The only .480 even mentioned is a .480 Gibbs, per Fleming:

"This cartridge appears in a Kynoch factory drawing date July 29, 1913. The drawing shows a case length of 3.15 inches, and a bullet weight of 520 grains. No examples of this rimless case, or rifles chambered for this cartridge are known to exist."