Hawg Haggen + 1
That's prettty much it, in a nut shell. Currently do not have a M/L that shoots better than my 1:66 in a 32" barrel with peep sights at 80 to 100 yds.
My Lyman shoots this kind of groups at 50yds. with PRB but selective on Conicals or Sabots and it has a 1:48.
I find your patch a bit interesting. Exactly what is it and how is it lubed? I like the print.
Go to Cain or Green Mountain and see what is available. I'm sure both can help. As far as a used barrel, good ones are hard to find, if not impossible. The last ones I saw, was on EBAY. While looking, perhaps you might want to include a .45 caliber.
Be Safe !!!