What you described may be the reason why I return back to shooting Real Black or Pyrodex.
It seems Blackhorn thrives with magnum powder loads - improves accuracy as the powder grain volume rises....... powder numbers that myself (and my bum right shoulder) are trying to avoid. Felt recoil of Blackhorn is in a different league from Real Black and Pyrodex.

You have a real nice 300 yards-capable load right now at 120 grains. Nice shooting!