I come from a Trad ML background, and while your idea has merit and may well be possible, I'll lay out a few inherant problems to consider;
Twist rate to stabilize round ball projectiles is
alot slower than what's found in CF rifles, a 1-48 is considered proper for the .32/.310 ball and 1-60 in the .45 range. Even guys with modern ML that are ment for sabots with 1-28/1-32 twists have trouble with
Patched ball unless they use really light loads and then are limited to 30-50 yard ranges before accuracy becomes a pattern instead of a group.
Off the shelf ball ment for ML's are made from pure or nearly pure lead,,meaning a really soft projectile. Thats needed so the patched ball will deformate a little and fit the rifling tight to recieve the proper spin. If a soft un-patched lead ball is used the fast twist CF rifling will foul with lead within 1 or two shots.
You could get molds and cast your own projectiles useing a harder lead mix, but if your going that route, might as well get molds designed for CF bullets, gas checks,,,,
maybe someone has better feed back for ya, but it's not gonna be as easy as "Gee, I'll shoot a couple round ball loads at the chipmunks, then just drop in my deer load with a copper jacket modern bullet",,