Butch,
Along with that Craigster posted, my understanding is that IMR4350 never was a military powder. It was introduced in 1940, and was partly developed for use in the .300 H&H, which Winchester had chambered in the Model 70 a few years earlier.
Hodgdon sold some of what they eventually called H4831 as "4350 data" powder very early on, because the powder could be safely used with IMR4350 handloading data, since H4831 was a little slower-burning.
