I read an article many years ago, might have been by someone now passed on, but the article concerned using IMR3031 instead of the faster burning powders in duplex loads.
This was due to the slower pressure curve of the 3031 which still did everything the faster powders did, as to velocity and clean burning.
I tested this in my Sharps, with an 1859 barrel that was lined and chambered for .50/70 by Sharps in the 1867 contract.
10gr. of 3031 and 60gr. of 1F BP worked perfectly in that old barrel and shot into 3" at 100meters, off sand bags.
3 of the impacts made a triangle shaped 1 1/2" group, inside the 3" triangle.
22" bl. from an 1868 conversion Sharps Carbine.
My action was a modern made Italian action of cast 4140.