Interesting thing about a ball - or bullet or arrow for that matter. When sub-sonic - they slow down VERY slowly, that is they lose very little speed over distance. A round ball started at 600fps is likely still making 500fps or maybe 525fps at 100yards. Would I use that for hunting - no way, just noting it. however, in a pistol, that 50gr. charge with a .700" round ball would certainly do for dispatching a wounded animal at very close range.
Standard barrel length for SXS rifles of the 19th century for hunting large and dangerous game in India was 22" to 26" depending on the size. The larger the bore - the shorter the barrels. Standard charges were in the mid range between 125gr. and 300gr., again, depending on bore size. The sporting powders of 1860 were much superior to ours even today - except maybe 2F or 3F Swiss. I think you will find a large bore will burn quite a bit of powder in very short barrel.
There is a side by side smoothbore sighted 4 bore on another web site being discussed right now - about 20" to 22" of barrel and 4 bore - 1.052" if true 4 bore. Standard load would be 8 to 12 drams with a round ball - ie: 218gr. to 328gr. with a ball running 5 to the pound, or 1,400gr. in pure lead.
My velocity increased at a steady rate from 60gr. to 165gr. in my 14 bore - 31" bl. To make Forsyth's drop figures, I had to use 165gr. 2F from 1986 to about 2004. After that time, I could get the same trajectories with 140gr.