Some inlines shoot patched round ball tolerably well. You have to monkey with the powder charge until the groups shrink.
This 5 shot group was fired at 50 yards from my old CVA StagHorn inline with 1/32" twist. The bore was not swabbed between shots. The powder charge was 80 grains of 3F Goex Pinnacle, patches were drill cloth lubed with Goop hand cleaner: