Rifleman. You are correct Forgett used a heavy rifle with the 200gr charges behind a 610 minie. The Buffalo Hunter that he used with the 577611 and 125gr is basically a cut down Zuave.
I agree with you, in general, regarding the use of the rifled musket and there isn't anything on the North American Continent that can't be laid low within reasonable ranges with 60gr of 2f behind a standard mini.
I only brought up the Forgett article because he used pure lead minis just having heavier skirts to resist deformation. Interesting that same book has an article regarding at what point the standard mini starts to deform.