There is something to be said for this. If one looks at a muzzleloader loading table, it is easy to see, starting at .54 caliber, and going up, more powder nets almost nothing.
Diminishing returns. The most responsive to heavier loadings is the .50 caliber. Going to 3F and 100 grains gives a
substantial velocity benift to the .50 caliber. In some cases, close to or right at 2000 fps. .54 or .58 doesn’t get anything. 10, maybe 15 fps.
Diminishing returns. If anyone doubts this, feel free to look it up. In fact, at the table I looked at, a .58 did over 100fps faster with 2F at the upper loadings.
What he wants to do can be done on the right day, at the right moment. I hope he pulls it off.
The hawken and being a .58 are significant barriers. The arc is too hard to account for drop. Accurately ranging and knowing what the hold over for that range is, well it could possibly be a drill in futility.
Now if a good shooter told me he can do it with a .50 long rifle with a 42” barrel, I could be convinced. Somewhat.