I have used a lightly lubed felt wad over powder, under patch and ball. I think it definitely removes some of the fouling allowing the bore to be consistent.
Works for me.
You're not going to hurt anything with a wad on top or a wad under it. Do whatever makes YOUR rifle shoot the best. Accuracy is the final test. Not what us yahoos have to say.
That being said, here is a video that does a good job explaining the differences, and how the Burton-Benton ball became the best performing of them all.
The Burton-Benton ball uses no wad, or anything for that matter, between the powder and slug.
Grooved expanding ball bullets (commonly called Minié balls) historically had the grooves filled with an anti-fouling agent. While today often referred to as a "lube" or "lubricant", it's actual purpose was to keep the fouling soft to enable continuous firing of the musket in combat. It is actually an anti-fouling agent.
The composition of this agent varied by time and place.
In the United States, in a report in 1856 on Experiments of Small Arms, the grease was composed of 1 part tallow to 3 parts beeswax:
The 1862 US Ordnance manual provided the following instructions for greasing expanding ball bullets with a mixture of 1 part tallow to 8 parts beeswax:
You'll note that it was not desirable to have grease in or on the bottom of the bullet. This is because the bottom of the powder chamber of the paper cartridges would bear against the bottom of the bullet, and it was not desired that the grease leach through the paper and ruin the powder on the other side of the paper bulkhead.
A properly sized and lubed (none in the base cavity) will clean the bore with each shot due to the scraping grooves of a proper Minnie ball. I have fired seventeen shots in rapid fire and had no reloading issues. I could have continued longer but the barrel got too hot to hold!
Don't over-think this. They had it all figured out by 1865.
I have tried using a lubed felt wad under a patched round ball to seal all the gasses behind the round ball so no gasses would escape around the patch. I don't shoot with a really tight patch to assist with loading. It really didn't give me better accuracy. I also thought it may help remove the bore fouling. I found a couple of the felt wads and they did look like they were somewhat effective and grabbing and removing the fouling. The felt was was fairly tight in the bore below the patched round ball.
Ohio Rusty ><>