I use 2.4 231 and 125gn bullet in 38 short colt brass, they have it now in stock at starline. Burns well in smaller case like 9mm.
https://www.starlinebrass.com/38-short-colt-brass
obviously for pistol only, load to spec for rifle in regular 38 brass.
I used the polish capper in the 2022 SASS Western Frontiersman Territorial and it worked well. I used one side to place the cap and the other to seat it. The capper something every cap and ball shooter should consider having.