Actually the 4831 mentioned was Hodgdon, specifically the surplus powder so designated. IMR's 4831 didn't appeared until the early 1970's, I believe.
I believe that this surplus powder was marketed as "4350 Data" powder. It was later called 4831. O'Connor's The Rifle Book , Second Ed., 1964, pg. 78, mentions DuPont 4350 thusly: ".., and of the powders now in use DuPont No. 4350 is the slowest burning of all."
