Ellis Lea wrote an article in American Rifleman in the "From the Loading Bench" column back in the 1980s. With a light projectile such as a round ball, you want a fast-burning powder, such as Bullseye, N310, 700-X, Red Dot or SR-7625.
In a .44 Magnum 5 grs. of Bullseye or 700-X or 6 grs. of Red Dot or SR-7625 is a good starting load. Work up as needed to get uniform velocities and good ignition. You will start getting leading and wild grouping in the .44 Magnum before you reach unsafe pressures. You are about right with 6-7 grains, I got lousy results trying to go over 8 grains in the .44 Magnum, I use 4 grs. of 7625 in the .38 Special with two .360 cast balls, or OOO buckshot.
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