Help Size Ball for Pistol

[RBK]

Got a EIBAR percussion pistol that measures 0.40 at muzzle and does not appear to be rifled. I was thinking of getting. 0.375 round lead balls and using 0.010 lubed patch. Is this a workable combination? I was considering 0.395 ball but that might be too tight with a patch. I can consult Pyrodex tables for powder loading also.
Many Thanks!

[Fatelvis]

Just rember to double your patch thickness. If you use a .015, instead of a .010, the .375 would probably work great.