The long action prototype in 256 Newton.
AFAIK, this is the only long action 1920 sporting rifle, the other 4 or 5 being military rifles chambered in 7x57, 30-06, and 303 British.
If you buy it, be aware that it is short chambered and it is listed in the R&D log as being chambered in 30-06. Among the previous owners were Mark Benenson, John Smyrl, and Bruce Jennings.