I tend to agree with that. From my research, they shot 60 grains behind the mini ball. There’s a whole thread on it here. I read the whole thing. Very good thread. Fully testing the 1853 Enfield before the war. More than 60 increased the recoil but had no velocity or accuracy benefits. Thus 60 grains of what we would consider to be 2F powder. I alluded to this earlier that increasing powder charge in a .58 will net mostly nothing. An 1853 musket had a longer and progressive rifling. Starting off as a slow spin and the further it got down the barrel, the rifling tightened up. Kinda brilliant. The musket had a long barrel. Unlike the hawken.What you should do is google how many grains of powder did a civil war soldier use in his Muzzle loader? You don't need 100 grains of powder.
I am going to say you are correct. You obviously have experience.