M.T.
Before I switched to the vegetable wads, I shot a few milk carton cards but not enough to ever determine if they worked for me. (milk / juice cartons are a pretty rare item here.) My barrels measure .4295" on both guns. I have shot sized bullets from .428 to .432 (from mold) without seeing any earth shaking results. I selected .431 because they "fill up" the chamber better....and they also fit in the Uberti pistols.
I have some 50/50 ww / lead alloy 215 bullets that according to LBT's hardness tester, test 14 BHN. These were the only bullets I have shot that left lots of lead slivers on the cleaning patch. (Shooting BP, I clean after every string of 6 or 8 shots) I have never tried straight ww.
And I just buy SPG. Weather permitting, I try to shoot daily and I have enough trouble casting enough bullets and keeping the cases clean. I have some DGL here but have never tried it because I think SPG works well.
I just looked at MVA's "Rough & Ready".
https://montanavintagearms.com/product/sights/mva/rough-ready-barrel-sight/ I toyed with the idea of drilling a hole in the Henry's rear sight and trying that but decided to go with the Soule because of the much longer sight radius, the windage adjustments and the Hadley cup. They are expensive but in my case, have been worth every penny.
Billy