6mm Lee Data
IMR powders changed formula at some point in the postwar era, c. 1960s if memory serves. I wouldn't use Sharpe's data at least for IMR powders as it predates WW2, and I would want more up-to-date data on the chance the other powders have changed.
Dave-
It would be really helpful if you could supply any reference for the change in IMR powders.
In the WWII era and slightly later, when surplus powders were available, many loads were published for some of the military powders, especially 4895, with the lot numbers specified. These were not the cannister powders released for reloaders by DuPont. Of course there is the confusion caused by Hodgdon's surplus powders having the same numbers as some of the DuPont IMR powders. That confusion has mostly cleared by now.
Some of the reloading literature from the 1950s and 1960s simply list the numbers, like 4895, 4831, etc., without specifying whether the powders are from DuPont/IMR, Hodgdon, or other source. While this is confusing and potentially hazardous, it does not indicate that the DuPont/IMR cannister powders changed.
If 3031 and 4064 have changed in any systematic way since Sharpe wrote, I'd really like to know about it.
Many thanks.
--Bob