At the range over the weekend, I had interesting results with the new .58 bore on the Pedersoli RMH. I don't have pictures of the groups yet, but will do my best to describe the process.
Starting the day, I shot the first three groups (85gr, 95gr and 105gr) with the Goex 2Fg I had in my horn. I was getting 2-4in groups at 50yds. Then the horn ran out and I had to
refill...with...Olde Eynsford 2F. I bought 10lbs of it several months ago. I thought this powder, made by Goex, would have similar results, so I pressed on. The 115gr group exploded (compared to the previous ones) out to 10-15" wide at 50yds. Walking downrange, I found the patches from this group were blown into 2-3 large pieces, almost completely shredded (the previous groups' patches were fine).
So, I started over. By the way, recoil against my upper arm, compared to my inner shoulder, was quite tolerable! Imagine that! This time I ran 90gr, 100gr, 110gr--where then the patches started shredding again.
Long story made short, 90gr (Olde Eynsford 2F) with .570 Hornady and .015 pillow ticking with mink oil lude appears to be the load. I was consistently getting one ragged hole at 50yds. Jumping up to 100gr opened the group significantly.
90gr of OE might be comparable to a larger amount of Goex 2Fg, right? Because as I
now know, OE is "quicker" and more energetic than standard Goex. Maybe I should investigate this patch-blowing issue at higher charges. I have some wasp's nest material in my range box I could try. Anyway, I'll go back to the range next weekend to fine tune, but I think this might be it. The season starts the weekend after next, so I'm feeling ready.