With that same bullet, cast of WWt with a dash of tin, sized .379 in my reformed 30-30 cases, WW std.LR primer, and 16-18 gr, IMR4227 I get satisfaction. This duplicates the old 38-55 High Velocity loading. My group size may not be meaningful to you, but if you can duplicate my load tell me what you think.
BTW, I wont use fillers (too much chance of ringed chambers) so make sure after you chamber a round to tip the muzzle up to settle the powder to the primer, lower and shoot. This will minimize shot to shot variation.
As for black powder, I have used it, but for me, I will stick with BP for my muzzle loaders and smokeless for cartridges.