First off, forget about shooting round balls, you will be wasteing your time.
Some TC Scout 50 calibers had a 1:20 twist. Not exactly your round ball set up.
I bought one of the first 50 cal. scouts when they came out and hunted with it up to last
year,put down many whitetails over the years.
I just got tired of tearing it apart everytime to clean it.
I ran a lot of different powders,bullets and sabots through that gun before I came up with
an accurate load that put deer down quickly.
What I ended up with and used for many years and never lost a deer was:
80 grs 2f Goex black
Barnes MZ sabot 250 gr.
CCI #11 magnum cap
Never knew what the velocity was for that load, but did put deer down very quickly.
The 250 gr MZ is a devastating bullet on deer, rarely going more than 25 yds.
It is a tight fit but goes down fairly well, in my testing the scout would not shoot
loose fitting sabots or all lead bullets.
Since I used that bullet for many years and had very good results, that was the first
sabot I tried in my TC Triumph, NOT, no way was that bullet going down that barrel.
But that's another story, good luck in your endeavor, TC