Every firearm, regardless of make and design, is an individual. It would be tough, if not iimpossible, to make such a generalization.
Besides, let's say that 24 grains of black powder is an accurate load in your .36 cap and ball.
Then you buy a conversion cylinder in .38 Long Colt, for that same revolver.
The .38 Long Colt case won't hold 24 grains of black powder.
You're also using a different bullet in the .36 cap and ball cylinder, compared to the type of bullet you'd load into a .38 Long Colt case.
Then there's bullet alloy: to avoid leading, use very soft or pure lead bullets with black powder. But with smokeless powder, you'd use a harder bullet.
Likewise, black powder requires a different kind of lubricant, made of natural ingredients such as tallow, beeswax, lard, Crisco and the like. Use petroleum products with black powder and you'll get a hard, tarry fouling.
Conversely, smokeless powder loads work best with petroleum-based lubricants, although some lubricants intended for black powder do work well with low-velocity smokeless loads. SPG and Lyman Black Gold come to mind.
The rifling construction and rate of twist may also come into play. Cap and ball revolvers have rifling designed to work best with lead balls, which have a very narrow band to grab the rifling.
Conical bullets, such as the typical bullet design, have much longer bearing surfaces for the rifling to grip.
This may affect accuracy and choice of bullet design.
There are many variables at work here, some of them seemingly opposed to each other. You may luck out and find a winning combination right away, or you may not. Some or a great deal of load development may be in order.
And, because each gun is an individual, what works in your revolver may not work in your buddy's, and vice-versa.
I don't own a conversion cylinder for any of my cap and ball revolvers. I have guns already made for cartridges, so I'm happy with using them. Perhaps someone with cylinder conversion experience can chime in here but I think I've given you a good overview of the different demands between cap and ball and cartridge guns, especially if different propellants are used.
