Coulda swore I replied to this yesterday, not sure where that went.
I shoot a .648 roundball in my Colerain 16ga smoothbore, with a .010 prelubed cotton patch. Anything thicker than that is tough enough loading that I'm afraid of bending the steel range rod! I have a 16ga rifled barrel that I'm working on now and plan on using the same .648 ball, but imagine with the rifling grooves I'll be able to use a thicker pillow ticking for patching.
Either way, 16's throw a hefty chunk of lead!