did I miss something?
IMO the discussion here is about loading a 10x60R Roth which is an old BP number, with some nitro substitutes, such as the historic R5 or a modern substitute.
In fact the 1940 RWS Handbook specifies R5 for the 9,3x72R (dimensions not so far away from 10x60R...), but as far as I can see only for the more potent nitro loads.