Jolly1, it is a fact of life, if you gain something you will lose something.
In this case, you gain a heavier projectile. But, you lose loading capacity. You will be trying to push a heavier projectile with less powder. In tests I have seen (there may be a You Tube video) a Ruger Old Army with max charge and round ball actually had an edge on the bullet (I have used both) with the lower possible max charge.
There is no harm with what you are considering. Just no real gain.
It is a fun game, do your own thing and enjoy.