As most of the answers to questions about ball size and loading information will begin with the "It depends" as the start of the answer.
With bare ball, the size will depend on how much fouling is in the barrel. You have also neglected to let us know what bore size you are shooting. Another aspect of the "It depends" part of the answer.
With smooth bores it is less likely that wiping between shots is anticipated. A bare ball can be close to bore size. With a patched ball you want the ball to be bore diameter less twice the compressed thickness of the patch. To load without a short starter then the ball should be 0.005 to 0.010" less than twice the compressed patch thickness.
A bare ball suggestion for load development would be 0.010" to 0.005" less than bore diameter.
Method 1: After loading the powder, start two over shot cards about a ball diameter into the bore. Load the ball and a final over shot card and run that stack to the breech. This method will scrape the fouling down the bore to be on top of the powder.
Method 2: Make a loose wad of tow or nest of jute or hemp twine about twice to three times the size of the ball with a very little bit of oil and after loading the powder, wrap the ball in the nest and start it in the barrel. Put a smaller nest on top and ram the wrapped ball to the breech. Use of the tow nest will allow for more shots before the bore needs to be wiped of fouling.
Sadly, I can't tell you which load will be more accurate. Your smoothbore gun will have to tell you.
