I am trying to develop a load for this 1877 rifle that was originally regulated for 3 3/4 dram of number 6 and paper patch bullet (no mention of size). I only assume that it was 300to 310.

Brass: jamison, fed 215 primer, swiss 1 1/2 : 120 Gr by volume, .3 card, 325 hand cast and lubed bullet.
At fifty yards , from a rest, 6 o'clock hold, registered 4 inches above and 3.75 from the left. The follow up shots the same as first. The third group was high and above the paper. I used a blow tube in between the shots.
your input will be much appreciated