I never shot White Hots and probably never will. Do yourself a favor, get a pound of Pyrodex RS in loose form. Try those same bullets with 80 grains of measured by volume powder (use a powder measure not a scale). And then see what your groups look like.

Between shots, take a clean patch and spritz it with Windex. Then swab the bore. After that run a dry patch, swabbing the bore the same way. Pyrodex and as most other powders, do leave fouling in the bore, but it is softer and easier to remove. Swab between shots and try that.. then post a picture at 25 yards. I bet you see the difference.

My CVA Staghorn Magnum loves 90 grains of Pyrodex RS and a powerbelt. Just a real nice shooting load.