Howdy
The correctly sized ball will be the one that shaves off a thin ring of lead when it is seated in the chamber. You need to shave off some lead to seal the ball in the chamber. You will know the correct size when you find it. No shaved ring and you have not sealed the chamber. Too much ring and it is too difficult to shove the ball into the chamber. You may shear one of the pivot pins in the linkage trying to force an overly large ball into the chamber.
When I bought my first C&B revolver in 1968, the lubed wool wads did not exist yet. Everybody slathered Crisco over the front of the chamber. In my experience, the Crisco in the chamber directly next to the one being fired was melted by the hot blast from the barrel/cylinder gap, and most of it dripped out of the chamber, being of no use at all. I blame this characteristic of using Crisco for lube directly for the chain fire I experienced one day. Many years later when I first heard about Wonder Wads, it was like sliced bread had been invented all over again. 1/4" or so of wool provides a much better spark arrester than a few thousandths of lead to steel seal and a thin layer of melted Crisco.
As far as being 'cheaper' to load your cartridges with Balck Powder, I dunno what you've been smoking, but I'd sure like to try some. Even though the pound for pound cost for BP is still cheaper than Smokeless, it is far offset by the amount of BP you dump into a cartridge case compared to how much Smokeless you dump in. Some guys use as little as 3 or 4 grains of various Smokeless for their loads. I use 7.5 grains of Unique in my 45 Colts, which last time I bought some was $16/pound. I use around 35 grains of Goex, which costs $14 over the counter around here. The best price I have gotten recently was when I bought half a case with a pard for around $11/pound.
Doing the math, I use about 5 1/2 cents worth of BP at the cheapest price I can find it per round, compared to around 1.7 cents per round with Unique. Now start investigating the cost of bullets lubed with BP comptible lube.
It's understandable that somebody from the flintlock and percussion rifle world would think that, how much BP do you go through in a year? I go through about 20 pounds when I shoot CAS. The guys in the local muzzle loading shop don't even like to see me come in the door. They can stretch a pound of powder for years. They can't understand why I'm hogging up the supply and buying 4 or 5 pounds at a time. We do a lot of shootin in CAS.