Ok just thinking out loud here

But I am considering a cap&ball revolver and watching a bunch of videos on them. And finding out that your use .451"-.454" balls in the .44 caliber ones. Guys either use a felt wad under the ball or apply grease on top of the ball for adding lube to the barrel and soften fouling and to prevent a chain fire.
Now my thinking out loud question: Why couldn't you use a .454" ball in a .45 rifle with a felt wad under it?
I imagine the answer will be because of the excess leading - but we use greased conicals?!? Hmmm

As the old saying goes "inquiring minds want to know"!