Hi ironoxoide, with the load that shot into one group(100gr.), mine was shooting into less than 1 1/2" for 6 shots 3-each. at 50yards - that was with 100gr.2G GOEX. As these then diverged at 100, still they were only 2" apart, with a 4-5" group total, which I figured that load would do just fine for target shooting work. It did that.

I noticed you were/are using a .010" patch. With a .562" ball, that patch will not make it to the bottom of the grooves & barely makes any pressure on the tops of the lands - combination totals .582". With a .580" bore, that's .001" tight on each land. I am not surprised this shot a huge pattern with a decent load - 120gr.
For me, that is not a load to even try - waste of powder and lead.
Even with the .574" ball, I used the .0215" ticking or the 10 ounce denim for patches that measured .022". The newer 10 ounce I am using in most of my rifles and smoothbore with patched ball, is .021" thick, compressed.
I use Track's (www.trackofthewolf.com) mink oil or Neetsfoot Oil for patch lube for hunting.

Good luck with the regulation. Shooting parallel is the most "perfect" regulation, however shooting together at 50yards is also good as most don't shoot ML's much beyond 100yards.

I sold my rifle as I wanted it for moose and my target load was in the 120gr. to 140gr. mark. It crossed badly with those loads. It would have worked OK for close range shooting with the 110gr. load, but I wanted to be able to shoot to at least 150yards and it would not do that for me.