Ned Roberts wrote a book back about a hundred years ago called "The Scheutzen Rifle", and gave loading data for lead bullet cartridges such as the 45-70, 38-55, 32-40, etc. About 1890 a fellow named Roland shot a group at 200 yards with one of these rifles which wasn't beaten until after WWII, as I recall. Anyway, one of the powders used in these cartridges was King's Semi-Smokless. I never saw any other reference to that powder in a lot of reading about early reloading, so I'll bet it wasn't made after WWI--You probable have something very rare.